Built-in Types
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The following sections describe the standard types that are built into the interpreter.
The principal built-in types are numerics, sequences, mappings, classes, instances and exceptions.
Some collection classes are mutable. The methods that add, subtract, or rearrange their members in place, and don’t return a specific item, never return the collection instance itself but None.
Some operations are supported by several object types; in particular, practically all objects can be compared for equality, tested for truth value, and converted to a string (with the function or the slightly different function). The latter function is implicitly used when an object is written by the function.
Any object can be tested for truth value, for use in an or condition or as operand of the Boolean operations below.
By default, an object is considered true unless its class defines either a method that returns False or a method that returns zero, when called with the object. Here are most of the built-in objects considered false:
constants defined to be false: None and False.
zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
empty sequences and collections: '', (), [], {}, set(), range(0)
Operations and built-in functions that have a Boolean result always return 0 or False for false and 1 or True for true, unless otherwise stated. (Important exception: the Boolean operations or and and always return one of their operands.)
and, or, notThese are the Boolean operations, ordered by ascending priority:
Operation
Result
Notes
x or y
if x is false, then y, else x
(1)
x and y
if x is false, then x, else y
(2)
not x
if x is false, then True, else False
(3)
Notes:
This is a short-circuit operator, so it only evaluates the second argument if the first one is false.
This is a short-circuit operator, so it only evaluates the second argument if the first one is true.
not has a lower priority than non-Boolean operators, so not a == b is interpreted as not (a == b), and a == not b is a syntax error.
There are eight comparison operations in Python. They all have the same priority (which is higher than that of the Boolean operations). Comparisons can be chained arbitrarily; for example, x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).
This table summarizes the comparison operations:
Operation
Meaning
<
strictly less than
<=
less than or equal
>
strictly greater than
>=
greater than or equal
==
equal
!=
not equal
is
object identity
is not
negated object identity
Numbers are created by numeric literals or as the result of built-in functions and operators. Unadorned integer literals (including hex, octal and binary numbers) yield integers. Numeric literals containing a decimal point or an exponent sign yield floating point numbers. Appending 'j' or 'J' to a numeric literal yields an imaginary number (a complex number with a zero real part) which you can add to an integer or float to get a complex number with real and imaginary parts.
Operation
Result
Notes
Full documentation
x + y
sum of x and y
x - y
difference of x and y
x * y
product of x and y
x / y
quotient of x and y
x // y
floored quotient of x and y
(1)
x % y
remainder of x / y
(2)
-x
x negated
+x
x unchanged
abs(x)
absolute value or magnitude of x
int(x)
x converted to integer
(3)(6)
float(x)
x converted to floating point
(4)(6)
complex(re, im)
a complex number with real part re, imaginary part im. im defaults to zero.
(6)
c.conjugate()
conjugate of the complex number c
divmod(x, y)
the pair (x // y, x % y)
(2)
pow(x, y)
x to the power y
(5)
x ** y
x to the power y
(5)
Notes:
Also referred to as integer division. The resultant value is a whole integer, though the result’s type is not necessarily int. The result is always rounded towards minus infinity: 1//2 is 0, (-1)//2 is -1, 1//(-2) is -1, and (-1)//(-2) is 0.
float also accepts the strings “nan” and “inf” with an optional prefix “+” or “-” for Not a Number (NaN) and positive or negative infinity.
Python defines pow(0, 0) and 0 ** 0 to be 1, as is common for programming languages.
The numeric literals accepted include the digits 0 to 9 or any Unicode equivalent (code points with the Nd property).
Operation
Result
x rounded to n digits, rounding half to even. If n is omitted, it defaults to 0.
Bitwise operations only make sense for integers. The result of bitwise operations is calculated as though carried out in two’s complement with an infinite number of sign bits.
The priorities of the binary bitwise operations are all lower than the numeric operations and higher than the comparisons; the unary operation ~ has the same priority as the other unary numeric operations (+ and -).
This table lists the bitwise operations sorted in ascending priority:
Operation
Result
Notes
x | y
bitwise or of x and y
(4)
x ^ y
bitwise exclusive or of x and y
(4)
x & y
bitwise and of x and y
(4)
x << n
x shifted left by n bits
(1)(2)
x >> n
x shifted right by n bits
(1)(3)
~x
the bits of x inverted
Notes:
A left shift by n bits is equivalent to multiplication by pow(2, n).
A right shift by n bits is equivalent to floor division by pow(2, n).
Performing these calculations with at least one extra sign extension bit in a finite two’s complement representation (a working bit-width of 1 + max(x.bit_length(), y.bit_length()) or more) is sufficient to get the same result as if there were an infinite number of sign bits.
Return the number of bits necessary to represent an integer in binary, excluding the sign and leading zeros:>>>
More precisely, if x is nonzero, then x.bit_length() is the unique positive integer k such that 2**(k-1) <= abs(x) < 2**k. Equivalently, when abs(x) is small enough to have a correctly rounded logarithm, then k = 1 + int(log(abs(x), 2)). If x is zero, then x.bit_length() returns 0.
Equivalent to:
New in version 3.1.int.to_bytes(length, byteorder, *, signed=False)
Return an array of bytes representing an integer.>>>
New in version 3.2.classmethod int.from_bytes(bytes, byteorder, *, signed=False)
Return the integer represented by the given array of bytes.>>>
The signed argument indicates whether two’s complement is used to represent the integer.
New in version 3.2.int.as_integer_ratio()
Return a pair of integers whose ratio is exactly equal to the original integer and with a positive denominator. The integer ratio of integers (whole numbers) is always the integer as the numerator and 1 as the denominator.
New in version 3.8.
Return True if the float instance is finite with integral value, and False otherwise:>>>
Two methods support conversion to and from hexadecimal strings. Since Python’s floats are stored internally as binary numbers, converting a float to or from a decimal string usually involves a small rounding error. In contrast, hexadecimal strings allow exact representation and specification of floating-point numbers. This can be useful when debugging, and in numerical work.float.hex()
Return a representation of a floating-point number as a hexadecimal string. For finite floating-point numbers, this representation will always include a leading 0x and a trailing p and exponent.classmethod float.fromhex(s)
Class method to return the float represented by a hexadecimal string s. The string s may have leading and trailing whitespace.
A hexadecimal string takes the form:
Note that the exponent is written in decimal rather than hexadecimal, and that it gives the power of 2 by which to multiply the coefficient. For example, the hexadecimal string 0x3.a7p10 represents the floating-point number (3 + 10./16 + 7./16**2) * 2.0**10, or 3740.0:>>>
Applying the reverse conversion to 3740.0 gives a different hexadecimal string representing the same number:>>>
CPython implementation detail: Currently, the prime used is P = 2**31 - 1 on machines with 32-bit C longs and P = 2**61 - 1 on machines with 64-bit C longs.
Here are the rules in detail:
If x = m / n is a nonnegative rational number and n is not divisible by P, define hash(x) as m * invmod(n, P) % P, where invmod(n, P) gives the inverse of n modulo P.
If x = m / n is a nonnegative rational number and n is divisible by P (but m is not) then n has no inverse modulo P and the rule above doesn’t apply; in this case define hash(x) to be the constant value sys.hash_info.inf.
If x = m / n is a negative rational number define hash(x) as -hash(-x). If the resulting hash is -1, replace it with -2.
The particular values sys.hash_info.inf, -sys.hash_info.inf and sys.hash_info.nan are used as hash values for positive infinity, negative infinity, or nans (respectively). (All hashable nans have the same hash value.)
Python supports a concept of iteration over containers. This is implemented using two distinct methods; these are used to allow user-defined classes to support iteration. Sequences, described below in more detail, always support the iteration methods.
One method needs to be defined for container objects to provide iteration support:container.__iter__()
The iterator objects themselves are required to support the following two methods, which together form the iterator protocol:iterator.__iter__()
Python defines several iterator objects to support iteration over general and specific sequence types, dictionaries, and other more specialized forms. The specific types are not important beyond their implementation of the iterator protocol.
This table lists the sequence operations sorted in ascending priority. In the table, s and t are sequences of the same type, n, i, j and k are integers and x is an arbitrary object that meets any type and value restrictions imposed by s.
Operation
Result
Notes
x in s
True if an item of s is equal to x, else False
(1)
x not in s
False if an item of s is equal to x, else True
(1)
s + t
the concatenation of s and t
(6)(7)
s * n or n * s
equivalent to adding s to itself n times
(2)(7)
s[i]
ith item of s, origin 0
(3)
s[i:j]
slice of s from i to j
(3)(4)
s[i:j:k]
slice of s from i to j with step k
(3)(5)
len(s)
length of s
min(s)
smallest item of s
max(s)
largest item of s
s.index(x[, i[, j]])
index of the first occurrence of x in s (at or after index i and before index j)
(8)
s.count(x)
total number of occurrences of x in s
Notes:
Values of n less than 0 are treated as 0 (which yields an empty sequence of the same type as s). Note that items in the sequence s are not copied; they are referenced multiple times. This often haunts new Python programmers; consider:>>>
What has happened is that [[]] is a one-element list containing an empty list, so all three elements of [[]] * 3 are references to this single empty list. Modifying any of the elements of lists modifies this single list. You can create a list of different lists this way:>>>
If i or j is negative, the index is relative to the end of sequence s: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.
The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.
The slice of s from i to j with step k is defined as the sequence of items with index x = i + n*k such that 0 <= n < (j-i)/k. In other words, the indices are i, i+k, i+2*k, i+3*k and so on, stopping when j is reached (but never including j). When k is positive, i and j are reduced to len(s) if they are greater. When k is negative, i and j are reduced to len(s) - 1 if they are greater. If i or j are omitted or None, they become “end” values (which end depends on the sign of k). Note, k cannot be zero. If k is None, it is treated like 1.
Concatenating immutable sequences always results in a new object. This means that building up a sequence by repeated concatenation will have a quadratic runtime cost in the total sequence length. To get a linear runtime cost, you must switch to one of the alternatives below:
for other types, investigate the relevant class documentation
Operation
Result
Notes
s[i] = x
item i of s is replaced by x
s[i:j] = t
slice of s from i to j is replaced by the contents of the iterable t
del s[i:j]
same as s[i:j] = []
s[i:j:k] = t
the elements of s[i:j:k] are replaced by those of t
(1)
del s[i:j:k]
removes the elements of s[i:j:k] from the list
s.append(x)
appends x to the end of the sequence (same as s[len(s):len(s)] = [x])
s.clear()
removes all items from s (same as del s[:])
(5)
s.copy()
creates a shallow copy of s (same as s[:])
(5)
s.extend(t) or s += t
extends s with the contents of t (for the most part the same as s[len(s):len(s)] = t)
s *= n
updates s with its contents repeated n times
(6)
s.insert(i, x)
inserts x into s at the index given by i (same as s[i:i] = [x])
s.pop() or s.pop(i)
retrieves the item at i and also removes it from s
(2)
s.remove(x)
remove the first item from s where s[i] is equal to x
(3)
s.reverse()
reverses the items of s in place
(4)
Notes:
t must have the same length as the slice it is replacing.
The optional argument i defaults to -1, so that by default the last item is removed and returned.
The reverse() method modifies the sequence in place for economy of space when reversing a large sequence. To remind users that it operates by side effect, it does not return the reversed sequence.
New in version 3.3: clear() and copy() methods.
Lists are mutable sequences, typically used to store collections of homogeneous items (where the precise degree of similarity will vary by application).class list([iterable])
Lists may be constructed in several ways:
Using a pair of square brackets to denote the empty list: []
Using square brackets, separating items with commas: [a], [a, b, c]
Using a list comprehension: [x for x in iterable]
Using the type constructor: list() or list(iterable)
The constructor builds a list whose items are the same and in the same order as iterable’s items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a list, a copy is made and returned, similar to iterable[:]. For example, list('abc') returns ['a', 'b', 'c'] and list( (1, 2, 3) ) returns [1, 2, 3]. If no argument is given, the constructor creates a new empty list, [].
This method sorts the list in place, using only < comparisons between items. Exceptions are not suppressed - if any comparison operations fail, the entire sort operation will fail (and the list will likely be left in a partially modified state).
key specifies a function of one argument that is used to extract a comparison key from each list element (for example, key=str.lower). The key corresponding to each item in the list is calculated once and then used for the entire sorting process. The default value of None means that list items are sorted directly without calculating a separate key value.
reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed.
Tuples may be constructed in a number of ways:
Using a pair of parentheses to denote the empty tuple: ()
Using a trailing comma for a singleton tuple: a, or (a,)
Separating items with commas: a, b, c or (a, b, c)
The constructor builds a tuple whose items are the same and in the same order as iterable’s items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a tuple, it is returned unchanged. For example, tuple('abc') returns ('a', 'b', 'c') and tuple( [1, 2, 3] ) returns (1, 2, 3). If no argument is given, the constructor creates a new empty tuple, ().
Note that it is actually the comma which makes a tuple, not the parentheses. The parentheses are optional, except in the empty tuple case, or when they are needed to avoid syntactic ambiguity. For example, f(a, b, c) is a function call with three arguments, while f((a, b, c)) is a function call with a 3-tuple as the sole argument.
For a positive step, the contents of a range r are determined by the formula r[i] = start + step*i where i >= 0 and r[i] < stop.
For a negative step, the contents of the range are still determined by the formula r[i] = start + step*i, but the constraints are i >= 0 and r[i] > stop.
A range object will be empty if r[0] does not meet the value constraint. Ranges do support negative indices, but these are interpreted as indexing from the end of the sequence determined by the positive indices.
Range examples:>>>
The value of the start parameter (or 0 if the parameter was not supplied)stop
The value of the stop parameterstep
The value of the step parameter (or 1 if the parameter was not supplied)
Changed in version 3.3: Define ‘==’ and ‘!=’ to compare range objects based on the sequence of values they define (instead of comparing based on object identity).
See also
Single quotes: 'allows embedded "double" quotes'
Double quotes: "allows embedded 'single' quotes".
Triple quoted: '''Three single quotes''', """Three double quotes"""
Triple quoted strings may span multiple lines - all associated whitespace will be included in the string literal.
String literals that are part of a single expression and have only whitespace between them will be implicitly converted to a single string literal. That is, ("spam " "eggs") == "spam eggs".
Since there is no separate “character” type, indexing a string produces strings of length 1. That is, for a non-empty string s, s[0] == s[0:1].
Changed in version 3.3: For backwards compatibility with the Python 2 series, the u prefix is once again permitted on string literals. It has no effect on the meaning of string literals and cannot be combined with the r prefix.class str(object='')class str(object=b'', encoding='utf-8', errors='strict')
Return a copy of the string with its first character capitalized and the rest lowercased.
Changed in version 3.8: The first character is now put into titlecase rather than uppercase. This means that characters like digraphs will only have their first letter capitalized, instead of the full character.str.casefold()
Return a casefolded copy of the string. Casefolded strings may be used for caseless matching.
The casefolding algorithm is described in section 3.13 of the Unicode Standard.
New in version 3.3.str.center(width[, fillchar])
Return centered in a string of length width. Padding is done using the specified fillchar (default is an ASCII space). The original string is returned if width is less than or equal to len(s).str.count(sub[, start[, end]])
Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.str.encode(encoding="utf-8", errors="strict")
Changed in version 3.1: Support for keyword arguments added.
Changed in version 3.9: The errors is now checked in development mode and in debug mode.str.endswith(suffix[, start[, end]])
Return True if the string ends with the specified suffix, otherwise return False. suffix can also be a tuple of suffixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.str.expandtabs(tabsize=8)
Return a copy of the string where all tab characters are replaced by one or more spaces, depending on the current column and the given tab size. Tab positions occur every tabsize characters (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the string, the current column is set to zero and the string is examined character by character. If the character is a tab (\t), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the character is a newline (\n) or return (\r), it is copied and the current column is reset to zero. Any other character is copied unchanged and the current column is incremented by one regardless of how the character is represented when printed.>>>
str.find(sub[, start[, end]])
Return the lowest index in the string where substring sub is found within the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.
Note
str.format(*args, **kwargs)
Perform a string formatting operation. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. Each replacement field contains either the numeric index of a positional argument, or the name of a keyword argument. Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument.>>>
Note
Changed in version 3.7: When formatting a number with the n type, the function sets temporarily the LC_CTYPE locale to the LC_NUMERIC locale in some cases.str.format_map(mapping)
New in version 3.2.str.index(sub[, start[, end]])
Return True if all characters in the string are alphanumeric and there is at least one character, False otherwise. A character c is alphanumeric if one of the following returns True: c.isalpha(), c.isdecimal(), c.isdigit(), or c.isnumeric().str.isalpha()
Return True if all characters in the string are alphabetic and there is at least one character, False otherwise. Alphabetic characters are those characters defined in the Unicode character database as “Letter”, i.e., those with general category property being one of “Lm”, “Lt”, “Lu”, “Ll”, or “Lo”. Note that this is different from the “Alphabetic” property defined in the Unicode Standard.str.isascii()
Return True if the string is empty or all characters in the string are ASCII, False otherwise. ASCII characters have code points in the range U+0000-U+007F.
New in version 3.7.str.isdecimal()
Return True if all characters in the string are decimal characters and there is at least one character, False otherwise. Decimal characters are those that can be used to form numbers in base 10, e.g. U+0660, ARABIC-INDIC DIGIT ZERO. Formally a decimal character is a character in the Unicode General Category “Nd”.str.isdigit()
Return True if all characters in the string are digits and there is at least one character, False otherwise. Digits include decimal characters and digits that need special handling, such as the compatibility superscript digits. This covers digits which cannot be used to form numbers in base 10, like the Kharosthi numbers. Formally, a digit is a character that has the property value Numeric_Type=Digit or Numeric_Type=Decimal.str.isidentifier()
Example:>>>
str.islower()
Return True if all characters in the string are numeric characters, and there is at least one character, False otherwise. Numeric characters include digit characters, and all characters that have the Unicode numeric value property, e.g. U+2155, VULGAR FRACTION ONE FIFTH. Formally, numeric characters are those with the property value Numeric_Type=Digit, Numeric_Type=Decimal or Numeric_Type=Numeric.str.isprintable()
Return True if there are only whitespace characters in the string and there is at least one character, False otherwise.
Return True if the string is a titlecased string and there is at least one character, for example uppercase characters may only follow uncased characters and lowercase characters only cased ones. Return False otherwise.str.isupper()
str.join(iterable)
Return the string left justified in a string of length width. Padding is done using the specified fillchar (default is an ASCII space). The original string is returned if width is less than or equal to len(s).str.lower()
The lowercasing algorithm used is described in section 3.13 of the Unicode Standard.str.lstrip([chars])
Return a copy of the string with leading characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix; rather, all combinations of its values are stripped:>>>
static str.maketrans(x[, y[, z]])
If there is only one argument, it must be a dictionary mapping Unicode ordinals (integers) or characters (strings of length 1) to Unicode ordinals, strings (of arbitrary lengths) or None. Character keys will then be converted to ordinals.
If there are two arguments, they must be strings of equal length, and in the resulting dictionary, each character in x will be mapped to the character at the same position in y. If there is a third argument, it must be a string, whose characters will be mapped to None in the result.str.partition(sep)
Split the string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.str.removeprefix(prefix, /)
If the string starts with the prefix string, return string[len(prefix):]. Otherwise, return a copy of the original string:>>>
New in version 3.9.str.removesuffix(suffix, /)
If the string ends with the suffix string and that suffix is not empty, return string[:-len(suffix)]. Otherwise, return a copy of the original string:>>>
New in version 3.9.str.replace(old, new[, count])
Return a copy of the string with all occurrences of substring old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.str.rfind(sub[, start[, end]])
Return the highest index in the string where substring sub is found, such that sub is contained within s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 on failure.str.rindex(sub[, start[, end]])
Return the string right justified in a string of length width. Padding is done using the specified fillchar (default is an ASCII space). The original string is returned if width is less than or equal to len(s).str.rpartition(sep)
Split the string at the last occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.str.rsplit(sep=None, maxsplit=-1)
Return a copy of the string with trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a suffix; rather, all combinations of its values are stripped:>>>
str.split(sep=None, maxsplit=-1)
Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified or -1, then there is no limit on the number of splits (all possible splits are made).
If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example, '1,,2'.split(',') returns ['1', '', '2']). The sep argument may consist of multiple characters (for example, '1<>2<>3'.split('<>') returns ['1', '2', '3']). Splitting an empty string with a specified separator returns [''].
For example:>>>
If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [].
For example:>>>
str.splitlines([keepends])
Return a list of the lines in the string, breaking at line boundaries. Line breaks are not included in the resulting list unless keepends is given and true.
Representation
Description
\n
Line Feed
\r
Carriage Return
\r\n
Carriage Return + Line Feed
\v or \x0b
Line Tabulation
\f or \x0c
Form Feed
\x1c
File Separator
\x1d
Group Separator
\x1e
Record Separator
\x85
Next Line (C1 Control Code)
\u2028
Line Separator
\u2029
Paragraph Separator
Changed in version 3.2: \v and \f added to list of line boundaries.
For example:>>>
For comparison, split('\n') gives:>>>
str.startswith(prefix[, start[, end]])
Return True if string starts with the prefix, otherwise return False. prefix can also be a tuple of prefixes to look for. With optional start, test string beginning at that position. With optional end, stop comparing string at that position.str.strip([chars])
Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped:>>>
The outermost leading and trailing chars argument values are stripped from the string. Characters are removed from the leading end until reaching a string character that is not contained in the set of characters in chars. A similar action takes place on the trailing end. For example:>>>
str.swapcase()
Return a copy of the string with uppercase characters converted to lowercase and vice versa. Note that it is not necessarily true that s.swapcase().swapcase() == s.str.title()
Return a titlecased version of the string where words start with an uppercase character and the remaining characters are lowercase.
For example:>>>
The algorithm uses a simple language-independent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result:>>>
A workaround for apostrophes can be constructed using regular expressions:>>>
str.translate(table)
The uppercasing algorithm used is described in section 3.13 of the Unicode Standard.str.zfill(width)
Return a copy of the string left filled with ASCII '0' digits to make a string of length width. A leading sign prefix ('+'/'-') is handled by inserting the padding after the sign character rather than before. The original string is returned if width is less than or equal to len(s).
For example:>>>
printf-style String FormattingNote
String objects have one unique built-in operation: the % operator (modulo). This is also known as the string formatting or interpolation operator. Given format % values (where format is a string), % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to using the sprintf() in the C language.
A conversion specifier contains two or more characters and has the following components, which must occur in this order:
The '%' character, which marks the start of the specifier.
Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename)).
Conversion flags (optional), which affect the result of some conversion types.
Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.
Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is read from the next element of the tuple in values, and the value to convert comes after the precision.
Length modifier (optional).
Conversion type.
When the right argument is a dictionary (or other mapping type), then the formats in the string must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example:>>>
In this case no * specifiers may occur in a format (since they require a sequential parameter list).
The conversion flag characters are:
Flag
Meaning
'#'
The value conversion will use the “alternate form” (where defined below).
'0'
The conversion will be zero padded for numeric values.
'-'
The converted value is left adjusted (overrides the '0' conversion if both are given).
' '
(a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.
'+'
A sign character ('+' or '-') will precede the conversion (overrides a “space” flag).
A length modifier (h, l, or L) may be present, but is ignored as it is not necessary for Python – so e.g. %ld is identical to %d.
The conversion types are:
Conversion
Meaning
Notes
'd'
Signed integer decimal.
'i'
Signed integer decimal.
'o'
Signed octal value.
(1)
'u'
Obsolete type – it is identical to 'd'.
(6)
'x'
Signed hexadecimal (lowercase).
(2)
'X'
Signed hexadecimal (uppercase).
(2)
'e'
Floating point exponential format (lowercase).
(3)
'E'
Floating point exponential format (uppercase).
(3)
'f'
Floating point decimal format.
(3)
'F'
Floating point decimal format.
(3)
'g'
Floating point format. Uses lowercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.
(4)
'G'
Floating point format. Uses uppercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.
(4)
'c'
Single character (accepts integer or single character string).
'r'
(5)
's'
(5)
'a'
(5)
'%'
No argument is converted, results in a '%' character in the result.
Notes:
The alternate form causes a leading octal specifier ('0o') to be inserted before the first digit.
The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.
The alternate form causes the result to always contain a decimal point, even if no digits follow it.
The precision determines the number of digits after the decimal point and defaults to 6.
The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.
The precision determines the number of significant digits before and after the decimal point and defaults to 6.
If precision is N, the output is truncated to N characters.
Since Python strings have an explicit length, %s conversions do not assume that '\0' is the end of the string.
Changed in version 3.1: %f conversions for numbers whose absolute value is over 1e50 are no longer replaced by %g conversions.
Bytes objects are immutable sequences of single bytes. Since many major binary protocols are based on the ASCII text encoding, bytes objects offer several methods that are only valid when working with ASCII compatible data and are closely related to string objects in a variety of other ways.class bytes([source[, encoding[, errors]]])
Firstly, the syntax for bytes literals is largely the same as that for string literals, except that a b prefix is added:
Single quotes: b'still allows embedded "double" quotes'
Double quotes: b"still allows embedded 'single' quotes".
Triple quoted: b'''3 single quotes''', b"""3 double quotes"""
Only ASCII characters are permitted in bytes literals (regardless of the declared source code encoding). Any binary values over 127 must be entered into bytes literals using the appropriate escape sequence.
In addition to the literal forms, bytes objects can be created in a number of other ways:
A zero-filled bytes object of a specified length: bytes(10)
From an iterable of integers: bytes(range(20))
Copying existing binary data via the buffer protocol: bytes(obj)
Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal numbers are a commonly used format for describing binary data. Accordingly, the bytes type has an additional class method to read data in that format:classmethod fromhex(string)
A reverse conversion function exists to transform a bytes object into its hexadecimal representation.hex([sep[, bytes_per_sep]])
Return a string object containing two hexadecimal digits for each byte in the instance.>>>
If you want to make the hex string easier to read, you can specify a single character separator sep parameter to include in the output. By default between each byte. A second optional bytes_per_sep parameter controls the spacing. Positive values calculate the separator position from the right, negative values from the left.>>>
New in version 3.5.
Since bytes objects are sequences of integers (akin to a tuple), for a bytes object b, b[0] will be an integer, while b[0:1] will be a bytes object of length 1. (This contrasts with text strings, where both indexing and slicing will produce a string of length 1)
The representation of bytes objects uses the literal format (b'...') since it is often more useful than e.g. bytes([46, 46, 46]). You can always convert a bytes object into a list of integers using list(b).
Note
For Python 2.x users: In the Python 2.x series, a variety of implicit conversions between 8-bit strings (the closest thing 2.x offers to a built-in binary data type) and Unicode strings were permitted. This was a backwards compatibility workaround to account for the fact that Python originally only supported 8-bit text, and Unicode text was a later addition. In Python 3.x, those implicit conversions are gone - conversions between 8-bit binary data and Unicode text must be explicit, and bytes and string objects will always compare unequal.
There is no dedicated literal syntax for bytearray objects, instead they are always created by calling the constructor:
Creating an empty instance: bytearray()
Creating a zero-filled instance with a given length: bytearray(10)
From an iterable of integers: bytearray(range(20))
Copying existing binary data via the buffer protocol: bytearray(b'Hi!')
Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal numbers are a commonly used format for describing binary data. Accordingly, the bytearray type has an additional class method to read data in that format:classmethod fromhex(string)
A reverse conversion function exists to transform a bytearray object into its hexadecimal representation.hex([sep[, bytes_per_sep]])
Return a string object containing two hexadecimal digits for each byte in the instance.>>>
New in version 3.5.
Since bytearray objects are sequences of integers (akin to a list), for a bytearray object b, b[0] will be an integer, while b[0:1] will be a bytearray object of length 1. (This contrasts with text strings, where both indexing and slicing will produce a string of length 1)
The representation of bytearray objects uses the bytes literal format (bytearray(b'...')) since it is often more useful than e.g. bytearray([46, 46, 46]). You can always convert a bytearray object into a list of integers using list(b).
Note
The methods on bytes and bytearray objects don’t accept strings as their arguments, just as the methods on strings don’t accept bytes as their arguments. For example, you have to write:
and:
Some bytes and bytearray operations assume the use of ASCII compatible binary formats, and hence should be avoided when working with arbitrary binary data. These restrictions are covered below.
Note
Using these ASCII based operations to manipulate binary data that is not stored in an ASCII based format may lead to data corruption.
The following methods on bytes and bytearray objects can be used with arbitrary binary data.bytes.count(sub[, start[, end]])bytearray.count(sub[, start[, end]])
Return the number of non-overlapping occurrences of subsequence sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.
Changed in version 3.3: Also accept an integer in the range 0 to 255 as the subsequence.bytes.removeprefix(prefix, /)bytearray.removeprefix(prefix, /)
If the binary data starts with the prefix string, return bytes[len(prefix):]. Otherwise, return a copy of the original binary data:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.
New in version 3.9.bytes.removesuffix(suffix, /)bytearray.removesuffix(suffix, /)
If the binary data ends with the suffix string and that suffix is not empty, return bytes[:-len(suffix)]. Otherwise, return a copy of the original binary data:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.
New in version 3.9.bytes.decode(encoding="utf-8", errors="strict")bytearray.decode(encoding="utf-8", errors="strict")
Note
Changed in version 3.1: Added support for keyword arguments.
Changed in version 3.9: The errors is now checked in development mode and in debug mode.bytes.endswith(suffix[, start[, end]])bytearray.endswith(suffix[, start[, end]])
Return True if the binary data ends with the specified suffix, otherwise return False. suffix can also be a tuple of suffixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.
Return the lowest index in the data where the subsequence sub is found, such that sub is contained in the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.
Note
Changed in version 3.3: Also accept an integer in the range 0 to 255 as the subsequence.bytes.index(sub[, start[, end]])bytearray.index(sub[, start[, end]])
Changed in version 3.3: Also accept an integer in the range 0 to 255 as the subsequence.bytes.join(iterable)bytearray.join(iterable)
New in version 3.1.bytes.partition(sep)bytearray.partition(sep)
Split the sequence at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing a copy of the original sequence, followed by two empty bytes or bytearray objects.
Return a copy of the sequence with all occurrences of subsequence old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.rfind(sub[, start[, end]])bytearray.rfind(sub[, start[, end]])
Return the highest index in the sequence where the subsequence sub is found, such that sub is contained within s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 on failure.
Changed in version 3.3: Also accept an integer in the range 0 to 255 as the subsequence.bytes.rindex(sub[, start[, end]])bytearray.rindex(sub[, start[, end]])
Changed in version 3.3: Also accept an integer in the range 0 to 255 as the subsequence.bytes.rpartition(sep)bytearray.rpartition(sep)
Split the sequence at the last occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty bytes or bytearray objects, followed by a copy of the original sequence.
Return True if the binary data starts with the specified prefix, otherwise return False. prefix can also be a tuple of prefixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.
Return a copy of the bytes or bytearray object where all bytes occurring in the optional argument delete are removed, and the remaining bytes have been mapped through the given translation table, which must be a bytes object of length 256.
Set the table argument to None for translations that only delete characters:>>>
Changed in version 3.6: delete is now supported as a keyword argument.
The following methods on bytes and bytearray objects have default behaviours that assume the use of ASCII compatible binary formats, but can still be used with arbitrary binary data by passing appropriate arguments. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.bytes.center(width[, fillbyte])bytearray.center(width[, fillbyte])
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.ljust(width[, fillbyte])bytearray.ljust(width[, fillbyte])
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.lstrip([chars])bytearray.lstrip([chars])
Return a copy of the sequence with specified leading bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None, the chars argument defaults to removing ASCII whitespace. The chars argument is not a prefix; rather, all combinations of its values are stripped:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.rjust(width[, fillbyte])bytearray.rjust(width[, fillbyte])
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.rsplit(sep=None, maxsplit=-1)bytearray.rsplit(sep=None, maxsplit=-1)
Return a copy of the sequence with specified trailing bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None, the chars argument defaults to removing ASCII whitespace. The chars argument is not a suffix; rather, all combinations of its values are stripped:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.split(sep=None, maxsplit=-1)bytearray.split(sep=None, maxsplit=-1)
Split the binary sequence into subsequences of the same type, using sep as the delimiter string. If maxsplit is given and non-negative, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified or is -1, then there is no limit on the number of splits (all possible splits are made).
For example:>>>
If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive ASCII whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the sequence has leading or trailing whitespace. Consequently, splitting an empty sequence or a sequence consisting solely of ASCII whitespace without a specified separator returns [].
For example:>>>
bytes.strip([chars])bytearray.strip([chars])
Return a copy of the sequence with specified leading and trailing bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None, the chars argument defaults to removing ASCII whitespace. The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.
The following methods on bytes and bytearray objects assume the use of ASCII compatible binary formats and should not be applied to arbitrary binary data. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.bytes.capitalize()bytearray.capitalize()
Return a copy of the sequence with each byte interpreted as an ASCII character, and the first byte capitalized and the rest lowercased. Non-ASCII byte values are passed through unchanged.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.expandtabs(tabsize=8)bytearray.expandtabs(tabsize=8)
Return a copy of the sequence where all ASCII tab characters are replaced by one or more ASCII spaces, depending on the current column and the given tab size. Tab positions occur every tabsize bytes (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the sequence, the current column is set to zero and the sequence is examined byte by byte. If the byte is an ASCII tab character (b'\t'), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the current byte is an ASCII newline (b'\n') or carriage return (b'\r'), it is copied and the current column is reset to zero. Any other byte value is copied unchanged and the current column is incremented by one regardless of how the byte value is represented when printed:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.isalnum()bytearray.isalnum()
Return True if all bytes in the sequence are alphabetical ASCII characters or ASCII decimal digits and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'. ASCII decimal digits are those byte values in the sequence b'0123456789'.
For example:>>>
bytes.isalpha()bytearray.isalpha()
Return True if all bytes in the sequence are alphabetic ASCII characters and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.
For example:>>>
bytes.isascii()bytearray.isascii()
Return True if the sequence is empty or all bytes in the sequence are ASCII, False otherwise. ASCII bytes are in the range 0-0x7F.
New in version 3.7.bytes.isdigit()bytearray.isdigit()
Return True if all bytes in the sequence are ASCII decimal digits and the sequence is not empty, False otherwise. ASCII decimal digits are those byte values in the sequence b'0123456789'.
For example:>>>
bytes.islower()bytearray.islower()
Return True if there is at least one lowercase ASCII character in the sequence and no uppercase ASCII characters, False otherwise.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.bytes.isspace()bytearray.isspace()
Return True if all bytes in the sequence are ASCII whitespace and the sequence is not empty, False otherwise. ASCII whitespace characters are those byte values in the sequence b' \t\n\r\x0b\f' (space, tab, newline, carriage return, vertical tab, form feed).bytes.istitle()bytearray.istitle()
For example:>>>
bytes.isupper()bytearray.isupper()
Return True if there is at least one uppercase alphabetic ASCII character in the sequence and no lowercase ASCII characters, False otherwise.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.bytes.lower()bytearray.lower()
Return a copy of the sequence with all the uppercase ASCII characters converted to their corresponding lowercase counterpart.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.splitlines(keepends=False)bytearray.splitlines(keepends=False)
For example:>>>
bytes.swapcase()bytearray.swapcase()
Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart and vice-versa.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.title()bytearray.title()
Return a titlecased version of the binary sequence where words start with an uppercase ASCII character and the remaining characters are lowercase. Uncased byte values are left unmodified.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. All other byte values are uncased.
The algorithm uses a simple language-independent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result:>>>
A workaround for apostrophes can be constructed using regular expressions:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.upper()bytearray.upper()
Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart.
For example:>>>
Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.bytes.zfill(width)bytearray.zfill(width)
For example:>>>
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.
printf-style Bytes FormattingNote
The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly). If the value being printed may be a tuple or dictionary, wrap it in a tuple.
Bytes objects (bytes/bytearray) have one unique built-in operation: the % operator (modulo). This is also known as the bytes formatting or interpolation operator. Given format % values (where format is a bytes object), % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to using the sprintf() in the C language.
A conversion specifier contains two or more characters and has the following components, which must occur in this order:
The '%' character, which marks the start of the specifier.
Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename)).
Conversion flags (optional), which affect the result of some conversion types.
Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.
Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is read from the next element of the tuple in values, and the value to convert comes after the precision.
Length modifier (optional).
Conversion type.
When the right argument is a dictionary (or other mapping type), then the formats in the bytes object must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example:>>>
In this case no * specifiers may occur in a format (since they require a sequential parameter list).
The conversion flag characters are:
Flag
Meaning
'#'
The value conversion will use the “alternate form” (where defined below).
'0'
The conversion will be zero padded for numeric values.
'-'
The converted value is left adjusted (overrides the '0' conversion if both are given).
' '
(a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.
'+'
A sign character ('+' or '-') will precede the conversion (overrides a “space” flag).
A length modifier (h, l, or L) may be present, but is ignored as it is not necessary for Python – so e.g. %ld is identical to %d.
The conversion types are:
Conversion
Meaning
Notes
'd'
Signed integer decimal.
'i'
Signed integer decimal.
'o'
Signed octal value.
(1)
'u'
Obsolete type – it is identical to 'd'.
(8)
'x'
Signed hexadecimal (lowercase).
(2)
'X'
Signed hexadecimal (uppercase).
(2)
'e'
Floating point exponential format (lowercase).
(3)
'E'
Floating point exponential format (uppercase).
(3)
'f'
Floating point decimal format.
(3)
'F'
Floating point decimal format.
(3)
'g'
Floating point format. Uses lowercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.
(4)
'G'
Floating point format. Uses uppercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.
(4)
'c'
Single byte (accepts integer or single byte objects).
'b'
(5)
's'
's' is an alias for 'b' and should only be used for Python2/3 code bases.
(6)
'a'
Bytes (converts any Python object using repr(obj).encode('ascii','backslashreplace)).
(5)
'r'
'r' is an alias for 'a' and should only be used for Python2/3 code bases.
(7)
'%'
No argument is converted, results in a '%' character in the result.
Notes:
The alternate form causes a leading octal specifier ('0o') to be inserted before the first digit.
The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.
The alternate form causes the result to always contain a decimal point, even if no digits follow it.
The precision determines the number of digits after the decimal point and defaults to 6.
The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.
The precision determines the number of significant digits before and after the decimal point and defaults to 6.
If precision is N, the output is truncated to N characters.
b'%s' is deprecated, but will not be removed during the 3.x series.
b'%r' is deprecated, but will not be removed during the 3.x series.
Note
The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.
See also
New in version 3.5.
Here is an example with a non-byte format:>>>
If the underlying object is writable, the memoryview supports one-dimensional slice assignment. Resizing is not allowed:>>>
One-dimensional memoryviews of hashable (read-only) types with formats ‘B’, ‘b’ or ‘c’ are also hashable. The hash is defined as hash(m) == hash(m.tobytes()):>>>
Changed in version 3.3: One-dimensional memoryviews can now be sliced. One-dimensional memoryviews with formats ‘B’, ‘b’ or ‘c’ are now hashable.
Changed in version 3.5: memoryviews can now be indexed with tuple of integers.
Note that, as with floating point numbers, v is w does not imply v == w for memoryview objects.
Changed in version 3.3: Previous versions compared the raw memory disregarding the item format and the logical array structure.tobytes(order=None)
New in version 3.8: order can be {‘C’, ‘F’, ‘A’}. When order is ‘C’ or ‘F’, the data of the original array is converted to C or Fortran order. For contiguous views, ‘A’ returns an exact copy of the physical memory. In particular, in-memory Fortran order is preserved. For non-contiguous views, the data is converted to C first. order=None is the same as order=’C’.hex([sep[, bytes_per_sep]])
Return a string object containing two hexadecimal digits for each byte in the buffer.>>>
New in version 3.5.
Return the data in the buffer as a list of elements.>>>
Return a readonly version of the memoryview object. The original memoryview object is unchanged.>>>
New in version 3.8.release()
The context management protocol can be used for a similar effect, using the with statement:>>>
New in version 3.2.cast(format[, shape])
Cast 1D/long to 1D/unsigned bytes:>>>
Cast 1D/unsigned bytes to 1D/char:>>>
Cast 1D/bytes to 3D/ints to 1D/signed char:>>>
Cast 1D/unsigned long to 2D/unsigned long:>>>
New in version 3.3.
Changed in version 3.5: The source format is no longer restricted when casting to a byte view.
There are also several readonly attributes available:obj
The underlying object of the memoryview:>>>
New in version 3.3.nbytes
nbytes == product(shape) * itemsize == len(m.tobytes()). This is the amount of space in bytes that the array would use in a contiguous representation. It is not necessarily equal to len(m):>>>
Multi-dimensional arrays:>>>
New in version 3.3.readonly
A bool indicating whether the memory is read only.format
Changed in version 3.3: format 'B' is now handled according to the struct module syntax. This means that memoryview(b'abc')[0] == b'abc'[0] == 97.itemsize
The size in bytes of each element of the memoryview:>>>
ndim
An integer indicating how many dimensions of a multi-dimensional array the memory represents.shape
Changed in version 3.3: An empty tuple instead of None when ndim = 0.strides
Changed in version 3.3: An empty tuple instead of None when ndim = 0.suboffsets
Used internally for PIL-style arrays. The value is informational only.c_contiguous
New in version 3.3.f_contiguous
New in version 3.3.contiguous
New in version 3.3.
Like other collections, sets support x in set, len(set), and for x in set. Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior.
The constructors for both classes work the same:class set([iterable])class frozenset([iterable])
Sets can be created by several means:
Use a comma-separated list of elements within braces: {'jack', 'sjoerd'}
Use a set comprehension: {c for c in 'abracadabra' if c not in 'abc'}
Use the type constructor: set(), set('foobar'), set(['a', 'b', 'foo'])
Return the number of elements in set s (cardinality of s).x in s
Test x for membership in s.x not in s
Test x for non-membership in s.isdisjoint(other)
Return True if the set has no elements in common with other. Sets are disjoint if and only if their intersection is the empty set.issubset(other)set <= other
Test whether every element in the set is in other.set < other
Test whether the set is a proper subset of other, that is, set <= other and set != other.issuperset(other)set >= other
Test whether every element in other is in the set.set > other
Test whether the set is a proper superset of other, that is, set >= other and set != other.union(*others)set | other | ...
Return a new set with elements from the set and all others.intersection(*others)set & other & ...
Return a new set with elements common to the set and all others.difference(*others)set - other - ...
Return a new set with elements in the set that are not in the others.symmetric_difference(other)set ^ other
Return a new set with elements in either the set or other but not both.copy()
Return a shallow copy of the set.
The subset and equality comparisons do not generalize to a total ordering function. For example, any two nonempty disjoint sets are not equal and are not subsets of each other, so all of the following return False: a<b, a==b, or a>b.
Update the set, adding elements from all others.intersection_update(*others)set &= other & ...
Update the set, keeping only elements found in it and all others.difference_update(*others)set -= other | ...
Update the set, removing elements found in others.symmetric_difference_update(other)set ^= other
Update the set, keeping only elements found in either set, but not in both.add(elem)
Add element elem to the set.remove(elem)
Remove element elem from the set if it is present.pop()
Remove all elements from the set.
Return a new dictionary initialized from an optional positional argument and a possibly empty set of keyword arguments.
Dictionaries can be created by several means:
Use a comma-separated list of key: value pairs within braces: {'jack': 4098, 'sjoerd': 4127} or {4098: 'jack', 4127: 'sjoerd'}
Use a dict comprehension: {}, {x: x ** 2 for x in range(10)}
Use the type constructor: dict(), dict([('foo', 100), ('bar', 200)]), dict(foo=100, bar=200)
If keyword arguments are given, the keyword arguments and their values are added to the dictionary created from the positional argument. If a key being added is already present, the value from the keyword argument replaces the value from the positional argument.
To illustrate, the following examples all return a dictionary equal to {"one": 1, "two": 2, "three": 3}:>>>
Providing keyword arguments as in the first example only works for keys that are valid Python identifiers. Otherwise, any valid keys can be used.
These are the operations that dictionaries support (and therefore, custom mapping types should support too):list(d)
Return a list of all the keys used in the dictionary d.len(d)
Return the number of items in the dictionary d.d[key]
Set d[key] to value.del d[key]
Return True if d has a key key, else False.key not in d
Equivalent to not key in d.iter(d)
Return an iterator over the keys of the dictionary. This is a shortcut for iter(d.keys()).clear()
Remove all items from the dictionary.copy()
Return a shallow copy of the dictionary.classmethod fromkeys(iterable[, value])
Create a new dictionary with keys from iterable and values set to value.
Remove and return a (key, value) pair from the dictionary. Pairs are returned in LIFO order.
Return a reverse iterator over the keys of the dictionary. This is a shortcut for reversed(d.keys()).
New in version 3.8.setdefault(key[, default])
If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.update([other])
Update the dictionary with the key/value pairs from other, overwriting existing keys. Return None.
An equality comparison between one dict.values() view and another will always return False. This also applies when comparing dict.values() to itself:>>>
d | other
Create a new dictionary with the merged keys and values of d and other, which must both be dictionaries. The values of other take priority when d and other share keys.
New in version 3.9.d |= other
New in version 3.9.
Dictionaries preserve insertion order. Note that updating a key does not affect the order. Keys added after deletion are inserted at the end.>>>
Changed in version 3.7: Dictionary order is guaranteed to be insertion order. This behavior was an implementation detail of CPython from 3.6.
Dictionaries and dictionary views are reversible.>>>
Changed in version 3.8: Dictionaries are now reversible.
See also
Dictionary views can be iterated over to yield their respective data, and support membership tests:len(dictview)
Return the number of entries in the dictionary.iter(dictview)
Return an iterator over the keys, values or items (represented as tuples of (key, value)) in the dictionary.
Changed in version 3.7: Dictionary order is guaranteed to be insertion order.x in dictview
Return True if x is in the underlying dictionary’s keys, values or items (in the latter case, x should be a (key, value) tuple).reversed(dictview)
Return a reverse iterator over the keys, values or items of the dictionary. The view will be iterated in reverse order of the insertion.
Changed in version 3.8: Dictionary views are now reversible.
An example of dictionary view usage:>>>
Note that there is no specific slot for any of these methods in the type structure for Python objects in the Python/C API. Extension types wanting to define these methods must provide them as a normal Python accessible method. Compared to the overhead of setting up the runtime context, the overhead of a single class dictionary lookup is negligible.
Note
Furthermore, parameterized generics erase type parameters during object creation:>>>
These standard library collections support parameterized generics.
All parameterized generics implement special read-only attributes.genericalias.__origin__
This attribute points at the non-parameterized generic class:>>>
genericalias.__args__
genericalias.__parameters__
This attribute is a lazily computed tuple (possibly empty) of unique type variables found in __args__:>>>
See also
New in version 3.9.
The interpreter supports several other kinds of objects. Most of these support only one or two operations.
Modules built into the interpreter are written like this: <module 'sys' (built-in)>. If loaded from a file, they are written as <module 'os' from '/usr/local/lib/pythonX.Y/os.pyc'>.
Function objects are created by function definitions. The only operation on a function object is to call it: func(argument-list).
There are really two flavors of function objects: built-in functions and user-defined functions. Both support the same operation (to call the function), but the implementation is different, hence the different object types.
Methods are functions that are called using the attribute notation. There are two flavors: built-in methods (such as append() on lists) and class instance methods. Built-in methods are described with the types that support them.
If you access a method (a function defined in a class namespace) through an instance, you get a special object: a bound method (also called instance method) object. When called, it will add the self argument to the argument list. Bound methods have two special read-only attributes: m.__self__ is the object on which the method operates, and m.__func__ is the function implementing the method. Calling m(arg-1, arg-2, ..., arg-n) is completely equivalent to calling m.__func__(m.__self__, arg-1, arg-2, ..., arg-n).
Types are written like this: <class 'int'>.
This object is returned by functions that don’t explicitly return a value. It supports no special operations. There is exactly one null object, named None (a built-in name). type(None)() produces the same singleton.
It is written as None.
It is written as Ellipsis or ....
It is written as NotImplemented.
They are written as False and True, respectively.
A dictionary or other mapping object used to store an object’s (writable) attributes.instance.__class__
The class to which a class instance belongs.class.__bases__
The tuple of base classes of a class object.definition.__name__
The name of the class, function, method, descriptor, or generator instance.definition.__qualname__
New in version 3.3.class.__mro__
This attribute is a tuple of classes that are considered when looking for base classes during method resolution.class.mro()
Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. The list is in definition order. Example:>>>
Objects of different types, except different numeric types, never compare equal. The == operator is always defined but for some object types (for example, class objects) is equivalent to . The <, <=, > and >= operators are only defined where they make sense; for example, they raise a exception when one of the arguments is a complex number.
Non-identical instances of a class normally compare as non-equal unless the class defines the method.
Instances of a class cannot be ordered with respect to other instances of the same class, or other types of object, unless the class defines enough of the methods , , , and (in general, and are sufficient, if you want the conventional meanings of the comparison operators).
The behavior of the and operators cannot be customized; also they can be applied to any two objects and never raise an exception.
Two more operations with the same syntactic priority, and , are supported by types that are or implement the method.
There are three distinct numeric types: integers, floating point numbers, and complex numbers. In addition, Booleans are a subtype of integers. Integers have unlimited precision. Floating point numbers are usually implemented using double in C; information about the precision and internal representation of floating point numbers for the machine on which your program is running is available in . Complex numbers have a real and imaginary part, which are each a floating point number. To extract these parts from a complex number z, use z.real and z.imag. (The standard library includes the additional numeric types , for rationals, and , for floating-point numbers with user-definable precision.)
Python fully supports mixed arithmetic: when a binary arithmetic operator has operands of different numeric types, the operand with the “narrower” type is widened to that of the other, where integer is narrower than floating point, which is narrower than complex. A comparison between numbers of different types behaves as though the exact values of those numbers were being compared.
The constructors , , and can be used to produce numbers of a specific type.
All numeric types (except complex) support the following operations (for priorities of the operations, see ):
Not for complex numbers. Instead convert to floats using if appropriate.
Conversion from floating point to integer may round or truncate as in C; see functions and for well-defined conversions.
See for a complete list of code points with the Nd property.
All types ( and ) also include the following operations:
x truncated to
the greatest <= x
the least >= x
For additional numeric operations see the and modules.
Negative shift counts are illegal and cause a to be raised.
The int type implements the . In addition, it provides a few more methods:int.bit_length()
The integer is represented using length bytes. An is raised if the integer is not representable with the given number of bytes.
The byteorder argument determines the byte order used to represent the integer. If byteorder is "big", the most significant byte is at the beginning of the byte array. If byteorder is "little", the most significant byte is at the end of the byte array. To request the native byte order of the host system, use as the byte order value.
The signed argument determines whether two’s complement is used to represent the integer. If signed is False and a negative integer is given, an is raised. The default value for signed is False.
The argument bytes must either be a or an iterable producing bytes.
The byteorder argument determines the byte order used to represent the integer. If byteorder is "big", the most significant byte is at the beginning of the byte array. If byteorder is "little", the most significant byte is at the end of the byte array. To request the native byte order of the host system, use as the byte order value.
The float type implements the . float also has the following additional methods.float.as_integer_ratio()
Return a pair of integers whose ratio is exactly equal to the original float and with a positive denominator. Raises on infinities and a on NaNs.float.is_integer()
Note that is an instance method, while is a class method.
where the optional sign may by either + or -, integer and fraction are strings of hexadecimal digits, and exponent is a decimal integer with an optional leading sign. Case is not significant, and there must be at least one hexadecimal digit in either the integer or the fraction. This syntax is similar to the syntax specified in section 6.4.4.2 of the C99 standard, and also to the syntax used in Java 1.5 onwards. In particular, the output of is usable as a hexadecimal floating-point literal in C or Java code, and hexadecimal strings produced by C’s %a format character or Java’s Double.toHexString are accepted by .
For numbers x and y, possibly of different types, it’s a requirement that hash(x) == hash(y) whenever x == y (see the method documentation for more details). For ease of implementation and efficiency across a variety of numeric types (including , , and ) Python’s hash for numeric types is based on a single mathematical function that’s defined for any rational number, and hence applies to all instances of and , and all finite instances of and . Essentially, this function is given by reduction modulo P for a fixed prime P. The value of P is made available to Python as the modulus attribute of .
For a number z, the hash values of the real and imaginary parts are combined by computing hash(z.real) + sys.hash_info.imag * hash(z.imag), reduced modulo 2**sys.hash_info.width so that it lies in range(-2**(sys.hash_info.width - 1), 2**(sys.hash_info.width - 1)). Again, if the result is -1, it’s replaced with -2.
To clarify the above rules, here’s some example Python code, equivalent to the built-in hash, for computing the hash of a rational number, , or :
Return an iterator object. The object is required to support the iterator protocol described below. If a container supports different types of iteration, additional methods can be provided to specifically request iterators for those iteration types. (An example of an object supporting multiple forms of iteration would be a tree structure which supports both breadth-first and depth-first traversal.) This method corresponds to the slot of the type structure for Python objects in the Python/C API.
Return the iterator object itself. This is required to allow both containers and iterators to be used with the and statements. This method corresponds to the slot of the type structure for Python objects in the Python/C API.iterator.__next__()
Return the next item from the container. If there are no further items, raise the exception. This method corresponds to the slot of the type structure for Python objects in the Python/C API.
Once an iterator’s method raises , it must continue to do so on subsequent calls. Implementations that do not obey this property are deemed broken.
Python’s s provide a convenient way to implement the iterator protocol. If a container object’s method is implemented as a generator, it will automatically return an iterator object (technically, a generator object) supplying the and methods. More information about generators can be found in .
There are three basic sequence types: lists, tuples, and range objects. Additional sequence types tailored for processing of and are described in dedicated sections.
The operations in the following table are supported by most sequence types, both mutable and immutable. The ABC is provided to make it easier to correctly implement these operations on custom sequence types.
The in and not in operations have the same priorities as the comparison operations. The + (concatenation) and * (repetition) operations have the same priority as the corresponding numeric operations.
Sequences of the same type also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length. (For full details see in the language reference.)
While the in and not in operations are used only for simple containment testing in the general case, some specialised sequences (such as , and ) also use them for subsequence testing:>>>
Further explanation is available in the FAQ entry .
if concatenating objects, you can build a list and use at the end or else write to an instance and retrieve its value when complete
if concatenating objects, you can similarly use or , or you can do in-place concatenation with a object. objects are mutable and have an efficient overallocation mechanism
if concatenating objects, extend a instead
Some sequence types (such as ) only support item sequences that follow specific patterns, and hence don’t support sequence concatenation or repetition.
index raises when x is not found in s. Not all implementations support passing the additional arguments i and j. These arguments allow efficient searching of subsections of the sequence. Passing the extra arguments is roughly equivalent to using s[i:j].index(x), only without copying any data and with the returned index being relative to the start of the sequence rather than the start of the slice.
The only operation that immutable sequence types generally implement that is not also implemented by mutable sequence types is support for the built-in.
This support allows immutable sequences, such as instances, to be used as keys and stored in and instances.
Attempting to hash an immutable sequence that contains unhashable values will result in .
The operations in the following table are defined on mutable sequence types. The ABC is provided to make it easier to correctly implement these operations on custom sequence types.
In the table s is an instance of a mutable sequence type, t is any iterable object and x is an arbitrary object that meets any type and value restrictions imposed by s (for example, only accepts integers that meet the value restriction 0 <= x <= 255).
remove() raises when x is not found in s.
clear() and copy() are included for consistency with the interfaces of mutable containers that don’t support slicing operations (such as and ). copy() is not part of the ABC, but most concrete mutable sequence classes provide it.
The value n is an integer, or an object implementing . Zero and negative values of n clear the sequence. Items in the sequence are not copied; they are referenced multiple times, as explained for s * n under .
Many other operations also produce lists, including the built-in.
Lists implement all of the and sequence operations. Lists also provide the following additional method:sort(*, key=None, reverse=False)
accepts two arguments that can only be passed by keyword ():
The utility is available to convert a 2.x style cmp function to a key function.
This method modifies the sequence in place for economy of space when sorting a large sequence. To remind users that it operates by side effect, it does not return the sorted sequence (use to explicitly request a new sorted list instance).
The method is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).
For sorting examples and a brief sorting tutorial, see .
CPython implementation detail: While a list is being sorted, the effect of attempting to mutate, or even inspect, the list is undefined. The C implementation of Python makes the list appear empty for the duration, and raises if it can detect that the list has been mutated during a sort.
Tuples are immutable sequences, typically used to store collections of heterogeneous data (such as the 2-tuples produced by the built-in). Tuples are also used for cases where an immutable sequence of homogeneous data is needed (such as allowing storage in a or instance).class tuple([iterable])
Using the built-in: tuple() or tuple(iterable)
Tuples implement all of the sequence operations.
For heterogeneous collections of data where access by name is clearer than access by index, may be a more appropriate choice than a simple tuple object.
The type represents an immutable sequence of numbers and is commonly used for looping a specific number of times in loops.class range(stop)class range(start, stop[, step])
The arguments to the range constructor must be integers (either built-in or any object that implements the __index__ special method). If the step argument is omitted, it defaults to 1. If the start argument is omitted, it defaults to 0. If step is zero, is raised.
Ranges containing absolute values larger than are permitted but some features (such as ) may raise .
Ranges implement all of the sequence operations except concatenation and repetition (due to the fact that range objects can only represent sequences that follow a strict pattern and repetition and concatenation will usually violate that pattern).start
The advantage of the type over a regular or is that a object will always take the same (small) amount of memory, no matter the size of the range it represents (as it only stores the start, stop and step values, calculating individual items and subranges as needed).
Range objects implement the ABC, and provide features such as containment tests, element index lookup, slicing and support for negative indices (see ):>>>
Testing range objects for equality with == and != compares them as sequences. That is, two range objects are considered equal if they represent the same sequence of values. (Note that two range objects that compare equal might have different , and attributes, for example range(0) == range(2, 1, 3) or range(0, 3, 2) == range(0, 4, 2).)
Changed in version 3.2: Implement the Sequence ABC. Support slicing and negative indices. Test objects for membership in constant time instead of iterating through all items.
New in version 3.3: The , and attributes.
The shows how to implement a lazy version of range suitable for floating point applications.
Textual data in Python is handled with objects, or strings. Strings are immutable of Unicode code points. String literals are written in a variety of ways:
See for more about the various forms of string literal, including supported escape sequences, and the r (“raw”) prefix that disables most escape sequence processing.
Strings may also be created from other objects using the constructor.
There is also no mutable string type, but or can be used to efficiently construct strings from multiple fragments.
Return a version of object. If object is not provided, returns the empty string. Otherwise, the behavior of str() depends on whether encoding or errors is given, as follows.
If neither encoding nor errors is given, str(object) returns , which is the “informal” or nicely printable string representation of object. For string objects, this is the string itself. If object does not have a method, then falls back to returning .
If at least one of encoding or errors is given, object should be a (e.g. or ). In this case, if object is a (or ) object, then str(bytes, encoding, errors) is equivalent to . Otherwise, the bytes object underlying the buffer object is obtained before calling . See and for information on buffer objects.
Passing a object to without the encoding or errors arguments falls under the first case of returning the informal string representation (see also the command-line option to Python). For example:>>>
For more information on the str class and its methods, see and the section below. To output formatted strings, see the and sections. In addition, see the section.
Strings implement all of the sequence operations, along with the additional methods described below.
Strings also support two styles of string formatting, one providing a large degree of flexibility and customization (see , and ) and the other based on C printf style formatting that handles a narrower range of types and is slightly harder to use correctly, but is often faster for the cases it can handle ().
The section of the standard library covers a number of other modules that provide various text related utilities (including regular expression support in the module).str.capitalize()
Casefolding is similar to lowercasing but more aggressive because it is intended to remove all case distinctions in a string. For example, the German lowercase letter 'ß' is equivalent to "ss". Since it is already lowercase, would do nothing to 'ß'; converts it to "ss".
Return an encoded version of the string as a bytes object. Default encoding is 'utf-8'. errors may be given to set a different error handling scheme. The default for errors is 'strict', meaning that encoding errors raise a . Other possible values are 'ignore', 'replace', 'xmlcharrefreplace', 'backslashreplace' and any other name registered via , see section . For a list of possible encodings, see section .
By default, the errors argument is not checked for best performances, but only used at the first encoding error. Enable the , or use a debug build to check errors.
The method should be used only if you need to know the position of sub. To check if sub is a substring or not, use the operator:>>>
See for a description of the various formatting options that can be specified in format strings.
When formatting a number (, , , and subclasses) with the n type (ex: '{:n}'.format(1234)), the function temporarily sets the LC_CTYPE locale to the LC_NUMERIC locale to decode decimal_point and thousands_sep fields of localeconv() if they are non-ASCII or longer than 1 byte, and the LC_NUMERIC locale is different than the LC_CTYPE locale. This temporary change affects other threads.
Similar to str.format(**mapping), except that mapping is used directly and not copied to a . This is useful if for example mapping is a dict subclass:>>>
Like , but raise when the substring is not found.str.isalnum()
Return True if the string is a valid identifier according to the language definition, section .
Call to test whether string s is a reserved identifier, such as and .
Return True if all cased characters in the string are lowercase and there is at least one cased character, False otherwise.str.isnumeric()
Return True if all characters in the string are printable or the string is empty, False otherwise. Nonprintable characters are those characters defined in the Unicode character database as “Other” or “Separator”, excepting the ASCII space (0x20) which is considered printable. (Note that printable characters in this context are those which should not be escaped when is invoked on a string. It has no bearing on the handling of strings written to or .)str.isspace()
A character is whitespace if in the Unicode character database (see ), either its general category is Zs (“Separator, space”), or its bidirectional class is one of WS, B, or S.str.istitle()
Return True if all cased characters in the string are uppercase and there is at least one cased character, False otherwise.>>>
Return a string which is the concatenation of the strings in iterable. A will be raised if there are any non-string values in iterable, including objects. The separator between elements is the string providing this method.str.ljust(width[, fillchar])
Return a copy of the string with all the cased characters converted to lowercase.
See for a method that will remove a single prefix string rather than all of a set of characters. For example:>>>
This static method returns a translation table usable for .
Like but raises when the substring sub is not found.str.rjust(width[, fillchar])
Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep is not specified or None, any whitespace string is a separator. Except for splitting from the right, behaves like which is described in detail below.str.rstrip([chars])
See for a method that will remove a single suffix string rather than all of a set of characters. For example:>>>
This method splits on the following line boundaries. In particular, the boundaries are a superset of .
Unlike when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:>>>
Return a copy of the string in which each character has been mapped through the given translation table. The table must be an object that implements indexing via , typically a or . When indexed by a Unicode ordinal (an integer), the table object can do any of the following: return a Unicode ordinal or a string, to map the character to one or more other characters; return None, to delete the character from the return string; or raise a exception, to map the character to itself.
You can use to create a translation map from character-to-character mappings in different formats.
See also the module for a more flexible approach to custom character mappings.str.upper()
Return a copy of the string with all the cased characters converted to uppercase. Note that s.upper().isupper() might be False if s contains uncased characters or if the Unicode category of the resulting character(s) is not “Lu” (Letter, uppercase), but e.g. “Lt” (Letter, titlecase).
The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly). Using the newer , the interface, or may help avoid these errors. Each of these alternatives provides their own trade-offs and benefits of simplicity, flexibility, and/or extensibility.
If format requires a single argument, values may be a single non-tuple object. Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).
String (converts any Python object using ).
String (converts any Python object using ).
String (converts any Python object using ).
See .
The core built-in types for manipulating binary data are and . They are supported by which uses the to access the memory of other binary objects without needing to make a copy.
The module supports efficient storage of basic data types like 32-bit integers and IEEE754 double-precision floating values.
As with string literals, bytes literals may also use a r prefix to disable processing of escape sequences. See for more about the various forms of bytes literal, including supported escape sequences.
While bytes literals and representations are based on ASCII text, bytes objects actually behave like immutable sequences of integers, with each value in the sequence restricted such that 0 <= x < 256 (attempts to violate this restriction will trigger ). This is done deliberately to emphasise that while many binary formats include ASCII based elements and can be usefully manipulated with some text-oriented algorithms, this is not generally the case for arbitrary binary data (blindly applying text processing algorithms to binary data formats that are not ASCII compatible will usually lead to data corruption).
Also see the built-in.
This class method returns a bytes object, decoding the given string object. The string must contain two hexadecimal digits per byte, with ASCII whitespace being ignored.>>>
Changed in version 3.7: now skips all ASCII whitespace in the string, not just spaces.
Changed in version 3.8: now supports optional sep and bytes_per_sep parameters to insert separators between bytes in the hex output.
objects are a mutable counterpart to objects.class bytearray([source[, encoding[, errors]]])
As bytearray objects are mutable, they support the sequence operations in addition to the common bytes and bytearray operations described in .
Also see the built-in.
This class method returns bytearray object, decoding the given string object. The string must contain two hexadecimal digits per byte, with ASCII whitespace being ignored.>>>
Changed in version 3.7: now skips all ASCII whitespace in the string, not just spaces.
Changed in version 3.8: Similar to , now supports optional sep and bytes_per_sep parameters to insert separators between bytes in the hex output.
Both bytes and bytearray objects support the sequence operations. They interoperate not just with operands of the same type, but with any . Due to this flexibility, they can be freely mixed in operations without causing errors. However, the return type of the result may depend on the order of operands.
The subsequence to search for may be any or an integer in the range 0 to 255.
The prefix may be any .
The suffix may be any .
Return a string decoded from the given bytes. Default encoding is 'utf-8'. errors may be given to set a different error handling scheme. The default for errors is 'strict', meaning that encoding errors raise a . Other possible values are 'ignore', 'replace' and any other name registered via , see section . For a list of possible encodings, see section .
By default, the errors argument is not checked for best performances, but only used at the first decoding error. Enable the , or use a debug build to check errors.
Passing the encoding argument to allows decoding any directly, without needing to make a temporary bytes or bytearray object.
The suffix(es) to search for may be any .bytes.find(sub[, start[, end]])bytearray.find(sub[, start[, end]])
The subsequence to search for may be any or an integer in the range 0 to 255.
The method should be used only if you need to know the position of sub. To check if sub is a substring or not, use the operator:>>>
Like , but raise when the subsequence is not found.
The subsequence to search for may be any or an integer in the range 0 to 255.
Return a bytes or bytearray object which is the concatenation of the binary data sequences in iterable. A will be raised if there are any values in iterable that are not , including objects. The separator between elements is the contents of the bytes or bytearray object providing this method.static bytes.maketrans(from, to)static bytearray.maketrans(from, to)
This static method returns a translation table usable for that will map each character in from into the character at the same position in to; from and to must both be and have the same length.
The separator to search for may be any .bytes.replace(old, new[, count])bytearray.replace(old, new[, count])
The subsequence to search for and its replacement may be any .
The subsequence to search for may be any or an integer in the range 0 to 255.
Like but raises when the subsequence sub is not found.
The subsequence to search for may be any or an integer in the range 0 to 255.
The separator to search for may be any .bytes.startswith(prefix[, start[, end]])bytearray.startswith(prefix[, start[, end]])
The prefix(es) to search for may be any .bytes.translate(table, /, delete=b'')bytearray.translate(table, /, delete=b'')
You can use the method to create a translation table.
Return a copy of the object centered in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For objects, the original sequence is returned if width is less than or equal to len(s).
Return a copy of the object left justified in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For objects, the original sequence is returned if width is less than or equal to len(s).
The binary sequence of byte values to remove may be any . See for a method that will remove a single prefix string rather than all of a set of characters. For example:>>>
Return a copy of the object right justified in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For objects, the original sequence is returned if width is less than or equal to len(s).
Split the binary sequence into subsequences of the same type, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep is not specified or None, any subsequence consisting solely of ASCII whitespace is a separator. Except for splitting from the right, behaves like which is described in detail below.bytes.rstrip([chars])bytearray.rstrip([chars])
The binary sequence of byte values to remove may be any . See for a method that will remove a single suffix string rather than all of a set of characters. For example:>>>
If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty subsequences (for example, b'1,,2'.split(b',') returns [b'1', b'', b'2']). The sep argument may consist of a multibyte sequence (for example, b'1<>2<>3'.split(b'<>') returns [b'1', b'2', b'3']). Splitting an empty sequence with a specified separator returns [b''] or [bytearray(b'')] depending on the type of object being split. The sep argument may be any .
The binary sequence of byte values to remove may be any .
Return True if the sequence is ASCII titlecase and the sequence is not empty, False otherwise. See for more details on the definition of “titlecase”.
Return a list of the lines in the binary sequence, breaking at ASCII line boundaries. This method uses the approach to splitting lines. Line breaks are not included in the resulting list unless keepends is given and true.
Unlike when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:>>>
Unlike , it is always the case that bin.swapcase().swapcase() == bin for the binary versions. Case conversions are symmetrical in ASCII, even though that is not generally true for arbitrary Unicode code points.
Return a copy of the sequence left filled with ASCII b'0' digits to make a sequence of length width. A leading sign prefix (b'+'/ b'-') is handled by inserting the padding after the sign character rather than before. For objects, the original sequence is returned if width is less than or equal to len(seq).
If format requires a single argument, values may be a single non-tuple object. Otherwise, values must be a tuple with exactly the number of items specified by the format bytes object, or a single mapping object (for example, a dictionary).
Bytes (any object that follows the or has ).
See .
- Adding % formatting to bytes and bytearray
objects allow Python code to access the internal data of an object that supports the without copying.class memoryview(object)
Create a that references object. object must support the buffer protocol. Built-in objects that support the buffer protocol include and .
A has the notion of an element, which is the atomic memory unit handled by the originating object. For many simple types such as and , an element is a single byte, but other types such as may have bigger elements.
len(view) is equal to the length of . If view.ndim = 0, the length is 1. If view.ndim = 1, the length is equal to the number of elements in the view. For higher dimensions, the length is equal to the length of the nested list representation of the view. The attribute will give you the number of bytes in a single element.
A supports slicing and indexing to expose its data. One-dimensional slicing will result in a subview:>>>
If is one of the native format specifiers from the module, indexing with an integer or a tuple of integers is also supported and returns a single element with the correct type. One-dimensional memoryviews can be indexed with an integer or a one-integer tuple. Multi-dimensional memoryviews can be indexed with tuples of exactly ndim integers where ndim is the number of dimensions. Zero-dimensional memoryviews can be indexed with the empty tuple.
Changed in version 3.4: memoryview is now registered automatically with
has several methods:__eq__(exporter)
A memoryview and a exporter are equal if their shapes are equivalent and if all corresponding values are equal when the operands’ respective format codes are interpreted using syntax.
For the subset of format strings currently supported by , v and w are equal if v.tolist() == w.tolist():>>>
If either format string is not supported by the module, then the objects will always compare as unequal (even if the format strings and buffer contents are identical):>>>
Return the data in the buffer as a bytestring. This is equivalent to calling the constructor on the memoryview.>>>
For non-contiguous arrays the result is equal to the flattened list representation with all elements converted to bytes. supports all format strings, including those that are not in module syntax.
Changed in version 3.8: Similar to , now supports optional sep and bytes_per_sep parameters to insert separators between bytes in the hex output.tolist()
Changed in version 3.3: now supports all single character native formats in module syntax as well as multi-dimensional representations.toreadonly()
Release the underlying buffer exposed by the memoryview object. Many objects take special actions when a view is held on them (for example, a would temporarily forbid resizing); therefore, calling release() is handy to remove these restrictions (and free any dangling resources) as soon as possible.
After this method has been called, any further operation on the view raises a (except itself which can be called multiple times):>>>
Cast a memoryview to a new format or shape. shape defaults to [byte_length//new_itemsize], which means that the result view will be one-dimensional. The return value is a new memoryview, but the buffer itself is not copied. Supported casts are 1D -> C- and C-contiguous -> 1D.
The destination format is restricted to a single element native format in syntax. One of the formats must be a byte format (‘B’, ‘b’ or ‘c’). The byte length of the result must be the same as the original length.
A string containing the format (in module style) for each element in the view. A memoryview can be created from exporters with arbitrary format strings, but some methods (e.g. ) are restricted to native single element formats.
A tuple of integers the length of giving the shape of the memory as an N-dimensional array.
A tuple of integers the length of giving the size in bytes to access each element for each dimension of the array.
A bool indicating whether the memory is C-.
A bool indicating whether the memory is Fortran .
A bool indicating whether the memory is .
A set object is an unordered collection of distinct objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. (For other containers see the built-in , , and classes, and the module.)
There are currently two built-in set types, and . The type is mutable — the contents can be changed using methods like add() and remove(). Since it is mutable, it has no hash value and cannot be used as either a dictionary key or as an element of another set. The type is immutable and — its contents cannot be altered after it is created; it can therefore be used as a dictionary key or as an element of another set.
Non-empty sets (not frozensets) can be created by placing a comma-separated list of elements within braces, for example: {'jack', 'sjoerd'}, in addition to the constructor.
Return a new set or frozenset object whose elements are taken from iterable. The elements of a set must be . To represent sets of sets, the inner sets must be objects. If iterable is not specified, a new empty set is returned.
Instances of and provide the following operations:len(s)
Note, the non-operator versions of , , , and , , and methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs').
Both and support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).
Instances of are compared to instances of based on their members. For example, set('abc') == frozenset('abc') returns True and so does set('abc') in set([frozenset('abc')]).
Since sets only define partial ordering (subset relationships), the output of the method is undefined for lists of sets.
Set elements, like dictionary keys, must be .
Binary operations that mix instances with return the type of the first operand. For example: frozenset('ab') | set('bc') returns an instance of .
The following table lists operations available for that do not apply to immutable instances of :update(*others)set |= other | ...
Remove element elem from the set. Raises if elem is not contained in the set.discard(elem)
Remove and return an arbitrary element from the set. Raises if the set is empty.clear()
Note, the non-operator versions of the , , , and methods will accept any iterable as an argument.
Note, the elem argument to the , , and methods may be a set. To support searching for an equivalent frozenset, a temporary one is created from elem.
A object maps values to arbitrary objects. Mappings are mutable objects. There is currently only one standard mapping type, the dictionary. (For other containers see the built-in , , and classes, and the module.)
A dictionary’s keys are almost arbitrary values. Values that are not , that is, values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys. Numeric types used for keys obey the normal rules for numeric comparison: if two numbers compare equal (such as 1 and 1.0) then they can be used interchangeably to index the same dictionary entry. (Note however, that since computers store floating-point numbers as approximations it is usually unwise to use them as dictionary keys.)
Dictionaries can be created by placing a comma-separated list of key: value pairs within braces, for example: {'jack': 4098, 'sjoerd': 4127} or {4098: 'jack', 4127: 'sjoerd'}, or by the constructor.class dict(**kwarg)class dict(mapping, **kwarg)class dict(iterable, **kwarg)
If no positional argument is given, an empty dictionary is created. If a positional argument is given and it is a mapping object, a dictionary is created with the same key-value pairs as the mapping object. Otherwise, the positional argument must be an object. Each item in the iterable must itself be an iterable with exactly two objects. The first object of each item becomes a key in the new dictionary, and the second object the corresponding value. If a key occurs more than once, the last value for that key becomes the corresponding value in the new dictionary.
Return the item of d with key key. Raises a if key is not in the map.
If a subclass of dict defines a method and key is not present, the d[key] operation calls that method with the key key as argument. The d[key] operation then returns or raises whatever is returned or raised by the __missing__(key) call. No other operations or methods invoke . If is not defined, is raised. must be a method; it cannot be an instance variable:>>>
The example above shows part of the implementation of . A different __missing__ method is used by .d[key] = value
Remove d[key] from d. Raises a if key is not in the map.key in d
is a class method that returns a new dictionary. value defaults to None. All of the values refer to just a single instance, so it generally doesn’t make sense for value to be a mutable object such as an empty list. To get distinct values, use a instead.get(key[, default])
Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a .items()
Return a new view of the dictionary’s items ((key, value) pairs). See the .keys()
Return a new view of the dictionary’s keys. See the .pop(key[, default])
If key is in the dictionary, remove it and return its value, else return default. If default is not given and key is not in the dictionary, a is raised.popitem()
is useful to destructively iterate over a dictionary, as often used in set algorithms. If the dictionary is empty, calling raises a .
Changed in version 3.7: LIFO order is now guaranteed. In prior versions, would return an arbitrary key/value pair.reversed(d)
accepts either another dictionary object or an iterable of key/value pairs (as tuples or other iterables of length two). If keyword arguments are specified, the dictionary is then updated with those key/value pairs: d.update(red=1, blue=2).values()
Return a new view of the dictionary’s values. See the .
Update the dictionary d with keys and values from other, which may be either a or an of key/value pairs. The values of other take priority when d and other share keys.
Dictionaries compare equal if and only if they have the same (key, value) pairs (regardless of ordering). Order comparisons (‘<’, ‘<=’, ‘>=’, ‘>’) raise .
can be used to create a read-only view of a .
The objects returned by , and are view objects. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes.
Keys and values are iterated over in insertion order. This allows the creation of (value, key) pairs using : pairs = zip(d.values(), d.keys()). Another way to create the same list is pairs = [(v, k) for (k, v) in d.items()].
Iterating views while adding or deleting entries in the dictionary may raise a or fail to iterate over all entries.
Keys views are set-like since their entries are unique and hashable. If all values are hashable, so that (key, value) pairs are unique and hashable, then the items view is also set-like. (Values views are not treated as set-like since the entries are generally not unique.) For set-like views, all of the operations defined for the abstract base class are available (for example, ==, <, or ^).
Python’s statement supports the concept of a runtime context defined by a context manager. This is implemented using a pair of methods that allow user-defined classes to define a runtime context that is entered before the statement body is executed and exited when the statement ends:contextmanager.__enter__()
Enter the runtime context and return either this object or another object related to the runtime context. The value returned by this method is bound to the identifier in the as clause of statements using this context manager.
An example of a context manager that returns itself is a . File objects return themselves from __enter__() to allow to be used as the context expression in a statement.
An example of a context manager that returns a related object is the one returned by . These managers set the active decimal context to a copy of the original decimal context and then return the copy. This allows changes to be made to the current decimal context in the body of the statement without affecting code outside the with statement.contextmanager.__exit__(exc_type, exc_val, exc_tb)
Exit the runtime context and return a Boolean flag indicating if any exception that occurred should be suppressed. If an exception occurred while executing the body of the statement, the arguments contain the exception type, value and traceback information. Otherwise, all three arguments are None.
Returning a true value from this method will cause the statement to suppress the exception and continue execution with the statement immediately following the with statement. Otherwise the exception continues propagating after this method has finished executing. Exceptions that occur during execution of this method will replace any exception that occurred in the body of the with statement.
The exception passed in should never be reraised explicitly - instead, this method should return a false value to indicate that the method completed successfully and does not want to suppress the raised exception. This allows context management code to easily detect whether or not an method has actually failed.
Python defines several context managers to support easy thread synchronisation, prompt closure of files or other objects, and simpler manipulation of the active decimal arithmetic context. The specific types are not treated specially beyond their implementation of the context management protocol. See the module for some examples.
Python’s s and the decorator provide a convenient way to implement these protocols. If a generator function is decorated with the decorator, it will return a context manager implementing the necessary and methods, rather than the iterator produced by an undecorated generator function.
GenericAlias objects are created by subscripting a class (usually a container), such as list[int]. They are intended primarily for .
Usually, the of container objects calls the method of the object. However, the subscription of some containers’ classes may call the classmethod of the class instead. The classmethod should return a GenericAlias object.
If the of the class’ metaclass is present, it will take precedence over the defined in the class (see for more details).
The GenericAlias object acts as a proxy for , implementing parameterized generics - a specific instance of a generic which provides the types for container elements.
The user-exposed type for the GenericAlias object can be accessed from and used for checks. It can also be used to create GenericAlias objects directly.T[X, Y, ...]
Creates a GenericAlias representing a type T containing elements of types X, Y, and more depending on the T used. For example, a function expecting a containing elements:
Another example for objects, using a , which is a generic type expecting two type parameters representing the key type and the value type. In this example, the function expects a dict with keys of type and values of type :
The builtin functions and do not accept GenericAlias types for their second argument:>>>
The Python runtime does not enforce . This extends to generic types and their type parameters. When creating an object from a GenericAlias, container elements are not checked against their type. For example, the following code is discouraged, but will run without errors:>>>
Calling or on a generic shows the parameterized type:>>>
The method of generics will raise an exception to disallow mistakes like dict[str][str]:>>>
However, such expressions are valid when are used. The index must have as many elements as there are type variable items in the GenericAlias object’s .>>>
This attribute is a (possibly of length 1) of generic types passed to the original of the generic container:>>>
– “Type Hinting Generics In Standard Collections”
– Used to implement parameterized generics.
– Generics in the module.
The only special operation on a module is attribute access: m.name, where m is a module and name accesses a name defined in m’s symbol table. Module attributes can be assigned to. (Note that the statement is not, strictly speaking, an operation on a module object; import foo does not require a module object named foo to exist, rather it requires an (external) definition for a module named foo somewhere.)
A special attribute of every module is . This is the dictionary containing the module’s symbol table. Modifying this dictionary will actually change the module’s symbol table, but direct assignment to the attribute is not possible (you can write m.__dict__['a'] = 1, which defines m.a to be 1, but you can’t write m.__dict__ = {}). Modifying directly is not recommended.
See and for these.
See for more information.
Like function objects, bound method objects support getting arbitrary attributes. However, since method attributes are actually stored on the underlying function object (meth.__func__), setting method attributes on bound methods is disallowed. Attempting to set an attribute on a method results in an being raised. In order to set a method attribute, you need to explicitly set it on the underlying function object:>>>
See for more information.
Code objects are used by the implementation to represent “pseudo-compiled” executable Python code such as a function body. They differ from function objects because they don’t contain a reference to their global execution environment. Code objects are returned by the built-in function and can be extracted from function objects through their __code__ attribute. See also the module.
Accessing __code__ raises an object.__getattr__ with arguments obj and "__code__".
A code object can be executed or evaluated by passing it (instead of a source string) to the or built-in functions.
See for more information.
Type objects represent the various object types. An object’s type is accessed by the built-in function . There are no special operations on types. The standard module defines names for all standard built-in types.
This object is commonly used by slicing (see ). It supports no special operations. There is exactly one ellipsis object, named (a built-in name). type(Ellipsis)() produces the singleton.
This object is returned from comparisons and binary operations when they are asked to operate on types they don’t support. See for more information. There is exactly one NotImplemented object. type(NotImplemented)() produces the singleton instance.
Boolean values are the two constant objects False and True. They are used to represent truth values (although other values can also be considered false or true). In numeric contexts (for example when used as the argument to an arithmetic operator), they behave like the integers 0 and 1, respectively. The built-in function can be used to convert any value to a Boolean, if the value can be interpreted as a truth value (see section above).
See for this information. It describes stack frame objects, traceback objects, and slice objects.
The implementation adds a few special read-only attributes to several object types, where they are relevant. Some of these are not reported by the built-in function.object.__dict__
The of the class, function, method, descriptor, or generator instance.
This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in .class.__subclasses__()