Leading whitespace (spaces and tabs) at the beginning of a logical line is used to compute the indentation level of the line, which in turn is used to determine the grouping of statements.
First, tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight (this is intended to be the same rule as used by Unix). The total number of spaces preceding the first non-blank character then determines the lineâs indentation. Indentation cannot be split over multiple physical lines using backslashes; the whitespace up to the first backslash determines the indentation.
Cross-platform compatibility note: because of the nature of text editors on non-UNIX platforms, it is unwise to use a mixture of spaces and tabs for the indentation in a single source file.
A formfeed character may be present at the start of the line; it will be ignored for the indentation calculations above. Formfeed characters occurring elsewhere in the leading whitespace have an undefined effect (for instance, they may reset the space count to zero).
The indentation levels of consecutive lines are used to generate INDENT and DEDENT tokens, using a stack, as follows.
Before the first line of the file is read, a single zero is pushed on the stack; this will never be popped off again. The numbers pushed on the stack will always be strictly increasing from bottom to top. At the beginning of each logical line, the lineâs indentation level is compared to the top of the stack. If it is equal, nothing happens. If it is larger, it is pushed on the stack, and one INDENT token is generated. If it is smaller, it must be one of the numbers occurring on the stack; all numbers on the stack that are larger are popped off, and for each number popped off a DEDENT token is generated. At the end of the file, a DEDENT token is generated for each number remaining on the stack that is larger than zero.
Here is an example of a correctly (though confusingly) indented piece of Python code:
def perm(l): # Compute the list of all permutations of l if len(l) <= 1: return [l] r = [] for i in range(len(l)): s = l[:i] + l[i+1:] p = perm(s) for x in p: r.append(l[i:i+1] + x) return r
The following example shows various indentation errors:
(Actually, the first three errors are detected by the parser; only the last error is found by the lexical analyzer â the indentation of return r does not match a level popped off the stack.)
· 15 min read
PEP8 : Python Enhancement Proposals, style-guide for Python.
print is the equivalent of console.log.
âprint() == console.log()â
# is used to make comments in your code.Python has a built in help function that letâs you see a description of the source code without having to navigate to it⊠â-SickNasty ⊠Autor Unknownâ
Python has three types of numbers:
Integer
Positive and Negative Counting Numbers.
No Decimal Point
Created by a literal non-decimal point number ⊠or ⊠with the int() constructor.
3. Complex Numbers
Consist of a real part and imaginary part.
If you came from a background in JavaScript and learned to accept the premise(s) of the following memeâŠ
Than I am sure you will find the means to suspend your disbelief.
The i is switched to a j in programming.
This is because the letter i is common place as the de facto index for any and all enumerable entities so it just makes sense not to compete for name-space when thereâs another 25 letters that donât get used for every loop under the sun. My most medium apologies to Leonhard Euler.
Type Casting : The process of converting one number to another.
The arithmetic operators are the same between JS and Python, with two additions:
â**â : Double asterisk for exponent.*
â//â : Integer Division.
There are no spaces between math operations in Python.
Integer Division gives the other part of the number from Module; it is a way to do round down numbers replacing
Python uses both single and double quotes.
You can escape strings like so 'Jodi asked, "What\\'s up, Sam?"'
Multiline strings use triple quotes.
Use the len() function to get the length of a string.
zero-based indexingPython letâs you use ranges
You can think of this as roughly equivalent to the slice method called on a JavaScript object or string⊠(mind you that in JS ⊠strings are wrapped in an object (under the hood)⊠upon which the string methods are actually called. As a immutable privative type by textbook definition, a string literal could not hope to invoke most of itâs methods without violating the state it was bound to on initialization if it were not for this bit of syntactic sugar.)
The end range is exclusive just like slice in JS.
The index string function is the equiv. of indexOf() in JS
The count function finds out how many times a substring appears in a string⊠pretty nifty for a hard coded feature of the language.
You can use + to concatenate strings, just like in JS.
You can also use ââ to repeat strings or multiply strings.**
Use the format() function to use placeholders in a string to input values later on.
Shorthand way to use format function is:print(f'Your name is {first_name} {last_name}')
Note that in JS join is used on an Array, in Python it is used on String.
There are also many handy testing methods.
Duck-Typing : Programming Style which avoids checking an objectâs type to figure out what it can do.
Duck Typing is the fundamental approach of Python.
Assignment of a value automatically declares a variable.
You can chain variable assignments to give multiple var names the same value.
NaN does not exist in Python, but you can âcreateâ it like so:print(float("nan"))
Python replaces null with none.
Using none is a convenient way to check to see why an action may not be operating correctly in your program.
One of the biggest benefits of Python is that it reads more like English than JS does.
By default, Python considers an object to be true UNLESS it is one of the following:
Constant None or False
Zero of any numeric type.
Python uses all the same equality operators as JS.
In Python, equality operators are processed from left to right.
Logical operators are processed in this order:
NOT
AND
OR
Just like in JS, you can use parentheses to change the inherent order of operations.Short Circuit : Stopping a program when a true or false has been reached.
In the Python community it is better to use is and is not over == or !=
If Statements*
if name == 'Monica': print('Hi, Monica.')if name == 'Monica': print('Hi, Monica.')else: print('Hello, stranger.')if name == 'Monica': print('Hi, Monica.')elif age < 12: print('You are not Monica, kiddo.')elif age > 2000: print('Unlike you, Monica is not an undead, immortal vampire.')elif age > 100: print('You are not Monica, grannie.')Remember the order of elif statements matter.
Break statement also exists in Python.
As are continue statements
Python equivalent to try/catch
You can name an error to give the output more specificity.
You can also use the pass commmand to by pass a certain error.
The pass method wonât allow you to bypass every single error so you can chain an exception series like so:
You can use an else statement to end a chain of except statements.
finally is used at the end to clean up all actions under any circumstance.
Using duck typing to check to see if some value is able to use a certain method.
Pass Keyword is required to write the JS equivalent of :
Function definition includes:
The def keyword
The name of the function
You can specify arguments by name without destructuring in Python.
The lambda keyword is used to create anonymous functions and are supposed to be one-liners.
toUpper = lambda s: s.upper()
Remember that in Python join() is called on a string with an array/list passed in as the argument.Python has a very powerful formatting engine.format() is also applied directly to strings.
**Python can be used to display html, css, and JS.**It is common to use Python as an API (Application Programming Interface)
ListTupleRangeCollections : Unordered data structures, hashable values.
Declared using one to three parameters.
Start : opt. default 0, first # in sequence.Stop : required next number past the last number in the sequence.Step : opt. default 1, difference between each number in the sequence.
Declared with curly braces of the built in dict()
Benefit of dictionaries in Python is that it doesnât matter how it is defined, if the keys and values are the same the dictionaries are considered equal.
Use the in operator to see if a key exists in a dictionary.
Sets : Unordered collection of distinct objects; objects that need to be hashable.
Always be unique, duplicate items are auto dropped from the set.
Removing DuplicatesMembership TestingMathematical Operators: Intersection, Union, Difference, Symmetric Difference.
Standard Set is mutable, Python has a immutable version called frozenset.Sets created by putting comma seperated values inside braces:
filter(function, iterable) : creates new iterable of the same type which includes each item for which the function returns true.
map(function, iterable) : creates new iterable of the same type which includes the result of calling the function on every item of the iterable.
sorted(iterable, key=None, reverse=False) : creates a new sorted list from the items in the iterable.
Output is always a list
key: opt function which coverts and item to a value to be compared.
reverse: optional boolean.
enumerate(iterable, start=0) : starts with a sequence and converts it to a series of tuples
zip(*iterables) : creates a zip object filled with tuples that combine 1 to 1 the items in each provided iterable.Functions that analyze iterable
len(iterable) : returns the count of the number of items.
max(args, key=None) : returns the largest of two or more arguments.
max(iterable, key=None) : returns the largest item in the iterable.
key optional function which converts an item to a value to be compared.min works the same way as max
sum(iterable) : used with a list of numbers to generate the total.
There is a faster way to concatenate an array of strings into one string, so do not use sum for that.
any(iterable) : returns True if any items in the iterable are true.
all(iterable) : returns True is all items in the iterable are true.
dir(dictionary) : returns the list of keys in the dictionary.Working with sets
Union : The pipe | operator or union(sets) function can be used to produce a new set which is a combination of all elements in the provided set.
Symmetric Difference : The ^ operator can be used to produce a new set of only the elements that appear in exactly one set and not in both.
Always Includes:
The for keyword2. A variable name3. The âinâ keyword4. An iterable of some kid5. A colon6. On the next line, an indented block of code called the for clause.
You can use break and continue statements inside for loops as well.
You can use the range function as the iterable for the for loop.
Common technique is to use the len() on a pre-defined list with a for loop to iterate over the indices of the list.
You can loop and destructure at the same time.
Prints 1, 2Prints 3, 4Prints 5, 6
You can use values() and keys() to loop over dictionaries.
Prints red
Prints 42
Prints color
Prints age
For loops can also iterate over both keys and values.
Getting tuples
Prints (âcolorâ, âredâ)
Prints (âageâ, 42)
Destructuring to values
Prints Key: age Value: 42
Prints Key: color Value: red
Looping over string
When you order arguments within a function or function call, the args need to occur in a particular order:
formal positional args.
args
keyword args with default values
kwargs
Modules are similar to packages in Node.jsCome in different types:
Built-In,
Third-Party,
Custom.
All loaded using import statements.
module : Python code in a separate file.package : Path to a directory that contains : Default file for a package.submodule : Another file in a moduleâs folder.function : Function in a module.
A module can be any file but it is usually created by placing a special file into a folder. pic
Try to avoid importing with wildcards in Python.
Use multiple lines for clarity when importing.
Python 3 removed <> and only uses !=
format() was introduced with P3
All strings in P3 are unicode and encoded.md5 was removed.
ConfigParser was renamed to configparsersets were killed in favor of set() class.
Keywords:
Leading whitespace (spaces and tabs) at the beginning of a logical line is used to compute the indentation level of the line, which in turn is used to determine the grouping of statements.
First, tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight (this is intended to be the same rule as used by Unix). The total number of spaces preceding the first non-blank character then determines the lineâs indentation. Indentation cannot be split over multiple physical lines using backslashes; the whitespace up to the first backslash determines the indentation.
Cross-platform compatibility note: because of the nature of text editors on non-UNIX platforms, it is unwise to use a mixture of spaces and tabs for the indentation in a single source file.
A formfeed character may be present at the start of the line; it will be ignored for the indentation calculations above. Formfeed characters occurring elsewhere in the leading whitespace have an undefined effect (for instance, they may reset the space count to zero).
The indentation levels of consecutive lines are used to generate INDENT and DEDENT tokens, using a stack, as follows.
Before the first line of the file is read, a single zero is pushed on the stack; this will never be popped off again. The numbers pushed on the stack will always be strictly increasing from bottom to top. At the beginning of each logical line, the lineâs indentation level is compared to the top of the stack. If it is equal, nothing happens. If it is larger, it is pushed on the stack, and one INDENT token is generated. If it is smaller, it must be one of the numbers occurring on the stack; all numbers on the stack that are larger are popped off, and for each number popped off a DEDENT token is generated. At the end of the file, a DEDENT token is generated for each number remaining on the stack that is larger than zero.
Here is an example of a correctly (though confusingly) indented piece of Python code:
def perm(l): # Compute the list of all permutations of l if len(l) <= 1: return [l] r = [] for i in range(len(l)): s = l[:i] + l[i+1:] p = perm(s) for x in p: r.append(l[i:i+1] + x) return r
The following example shows various indentation errors:
(Actually, the first three errors are detected by the parser; only the last error is found by the lexical analyzer â the indentation of return r does not match a level popped off the stack.)
PEP8 : Python Enhancement Proposals, style-guide for Python.
print is the equivalent of console.log.
âprint() == console.log()â
# is used to make comments in your code.Python has a built in help function that letâs you see a description of the source code without having to navigate to it⊠â-SickNasty ⊠Autor Unknownâ
Python has three types of numbers:
Integer
Positive and Negative Counting Numbers.
No Decimal Point
Created by a literal non-decimal point number ⊠or ⊠with the int() constructor.
3. Complex Numbers
Consist of a real part and imaginary part.
If you came from a background in JavaScript and learned to accept the premise(s) of the following memeâŠ
Than I am sure you will find the means to suspend your disbelief.
The i is switched to a j in programming.
This is because the letter i is common place as the de facto index for any and all enumerable entities so it just makes sense not to compete for name-space when thereâs another 25 letters that donât get used for every loop under the sun. My most medium apologies to Leonhard Euler.
Type Casting : The process of converting one number to another.
The arithmetic operators are the same between JS and Python, with two additions:
â**â : Double asterisk for exponent.*
â//â : Integer Division.
There are no spaces between math operations in Python.
Integer Division gives the other part of the number from Module; it is a way to do round down numbers replacing
Python uses both single and double quotes.
You can escape strings like so 'Jodi asked, "What\\'s up, Sam?"'
Multiline strings use triple quotes.
Use the len() function to get the length of a string.
zero-based indexingPython letâs you use ranges
You can think of this as roughly equivalent to the slice method called on a JavaScript object or string⊠(mind you that in JS ⊠strings are wrapped in an object (under the hood)⊠upon which the string methods are actually called. As a immutable privative type by textbook definition, a string literal could not hope to invoke most of itâs methods without violating the state it was bound to on initialization if it were not for this bit of syntactic sugar.)
The end range is exclusive just like slice in JS.
The index string function is the equiv. of indexOf() in JS
The count function finds out how many times a substring appears in a string⊠pretty nifty for a hard coded feature of the language.
You can use + to concatenate strings, just like in JS.
You can also use ââ to repeat strings or multiply strings.**
Use the format() function to use placeholders in a string to input values later on.
Shorthand way to use format function is:print(f'Your name is {first_name} {last_name}')
Note that in JS join is used on an Array, in Python it is used on String.
There are also many handy testing methods.
Duck-Typing : Programming Style which avoids checking an objectâs type to figure out what it can do.
Duck Typing is the fundamental approach of Python.
Assignment of a value automatically declares a variable.
You can chain variable assignments to give multiple var names the same value.
NaN does not exist in Python, but you can âcreateâ it like so:print(float("nan"))
Python replaces null with none.
Using none is a convenient way to check to see why an action may not be operating correctly in your program.
One of the biggest benefits of Python is that it reads more like English than JS does.
By default, Python considers an object to be true UNLESS it is one of the following:
Constant None or False
Zero of any numeric type.
Python uses all the same equality operators as JS.
In Python, equality operators are processed from left to right.
Logical operators are processed in this order:
NOT
AND
OR
Just like in JS, you can use parentheses to change the inherent order of operations.Short Circuit : Stopping a program when a true or false has been reached.
In the Python community it is better to use is and is not over == or !=
If Statements*
if name == 'Monica': print('Hi, Monica.')if name == 'Monica': print('Hi, Monica.')else: print('Hello, stranger.')if name == 'Monica': print('Hi, Monica.')elif age < 12: print('You are not Monica, kiddo.')elif age > 2000: print('Unlike you, Monica is not an undead, immortal vampire.')elif age > 100: print('You are not Monica, grannie.')Remember the order of elif statements matter.
Break statement also exists in Python.
As are continue statements
Python equivalent to try/catch
You can name an error to give the output more specificity.
You can also use the pass commmand to by pass a certain error.
The pass method wonât allow you to bypass every single error so you can chain an exception series like so:
You can use an else statement to end a chain of except statements.
finally is used at the end to clean up all actions under any circumstance.
Using duck typing to check to see if some value is able to use a certain method.
Pass Keyword is required to write the JS equivalent of :
Function definition includes:
The def keyword
The name of the function
You can specify arguments by name without destructuring in Python.
The lambda keyword is used to create anonymous functions and are supposed to be one-liners.
toUpper = lambda s: s.upper()
Remember that in Python join() is called on a string with an array/list passed in as the argument.Python has a very powerful formatting engine.format() is also applied directly to strings.
**Python can be used to display html, css, and JS.**It is common to use Python as an API (Application Programming Interface)
ListTupleRangeCollections : Unordered data structures, hashable values.
Declared using one to three parameters.
Start : opt. default 0, first # in sequence.Stop : required next number past the last number in the sequence.Step : opt. default 1, difference between each number in the sequence.
Declared with curly braces of the built in dict()
Benefit of dictionaries in Python is that it doesnât matter how it is defined, if the keys and values are the same the dictionaries are considered equal.
Use the in operator to see if a key exists in a dictionary.
Sets : Unordered collection of distinct objects; objects that need to be hashable.
Always be unique, duplicate items are auto dropped from the set.
Removing DuplicatesMembership TestingMathematical Operators: Intersection, Union, Difference, Symmetric Difference.
Standard Set is mutable, Python has a immutable version called frozenset.Sets created by putting comma seperated values inside braces:
filter(function, iterable) : creates new iterable of the same type which includes each item for which the function returns true.
map(function, iterable) : creates new iterable of the same type which includes the result of calling the function on every item of the iterable.
sorted(iterable, key=None, reverse=False) : creates a new sorted list from the items in the iterable.
Output is always a list
key: opt function which coverts and item to a value to be compared.
reverse: optional boolean.
enumerate(iterable, start=0) : starts with a sequence and converts it to a series of tuples
zip(*iterables) : creates a zip object filled with tuples that combine 1 to 1 the items in each provided iterable.Functions that analyze iterable
len(iterable) : returns the count of the number of items.
max(args, key=None) : returns the largest of two or more arguments.
max(iterable, key=None) : returns the largest item in the iterable.
key optional function which converts an item to a value to be compared.min works the same way as max
sum(iterable) : used with a list of numbers to generate the total.
There is a faster way to concatenate an array of strings into one string, so do not use sum for that.
any(iterable) : returns True if any items in the iterable are true.
all(iterable) : returns True is all items in the iterable are true.
dir(dictionary) : returns the list of keys in the dictionary.Working with sets
Union : The pipe | operator or union(sets) function can be used to produce a new set which is a combination of all elements in the provided set.
Symmetric Difference : The ^ operator can be used to produce a new set of only the elements that appear in exactly one set and not in both.
Always Includes:
The for keyword2. A variable name3. The âinâ keyword4. An iterable of some kid5. A colon6. On the next line, an indented block of code called the for clause.
You can use break and continue statements inside for loops as well.
You can use the range function as the iterable for the for loop.
Common technique is to use the len() on a pre-defined list with a for loop to iterate over the indices of the list.
You can loop and destructure at the same time.
Prints 1, 2Prints 3, 4Prints 5, 6
You can use values() and keys() to loop over dictionaries.
Prints red
Prints 42
Prints color
Prints age
For loops can also iterate over both keys and values.
Getting tuples
Prints (âcolorâ, âredâ)
Prints (âageâ, 42)
Destructuring to values
Prints Key: age Value: 42
Prints Key: color Value: red
Looping over string
When you order arguments within a function or function call, the args need to occur in a particular order:
formal positional args.
args
keyword args with default values
kwargs
Modules are similar to packages in Node.jsCome in different types:
Built-In,
Third-Party,
Custom.
All loaded using import statements.
module : Python code in a separate file.package : Path to a directory that contains : Default file for a package.submodule : Another file in a moduleâs folder.function : Function in a module.
A module can be any file but it is usually created by placing a special file into a folder. pic
Try to avoid importing with wildcards in Python.
Use multiple lines for clarity when importing.
Python 3 removed <> and only uses !=
format() was introduced with P3
All strings in P3 are unicode and encoded.md5 was removed.
ConfigParser was renamed to configparsersets were killed in favor of set() class.
Math.floor()There are no ++ and `` in Python, the only shorthand operators are:
none is an object and can be directly assigned to a variable.True and False must be capitalized
A colon at the end of the line.
One tab indentation for the code to run.
You can use default parameters just like in JS
Math.floor()There are no ++ and `` in Python, the only shorthand operators are:
none is an object and can be directly assigned to a variable.True and False must be capitalized
A colon at the end of the line.
One tab indentation for the code to run.
You can use default parameters just like in JS
***and del for is raiseassert elif from lambda returnbreak else global not tryclass except if or whilecontinue exec import passdef finally in print*** `def perm(l): # error: first line indented
for i in range(len(l)): # error: not indented
s = l[:i] + l[i+1:]
p = perm(l[:i] + l[i+1:]) # error: unexpected indent
for x in p:
r.append(l[i:i+1] + x)
return r # error: inconsistent dedent`def foo():
"""
The foo function does many amazing things that you
should not question. Just accept that it exists and
use it with caution.
"""
secretThing()print(3) # => 3
print(int(19)) # => 19
print(int()) # => 0print(2.24) # => 2.24
print(2.) # => 2.0
print(float()) # => 0.0
print(27e-5) # => 0.00027print(7j) # => 7j
print(5.1+7.7j)) # => 5.1+7.7j
print(complex(3, 5)) # => 3+5j
print(complex(17)) # => 17+0j
print(complex()) # => 0j# Using Float
print(17) # => 17
print(float(17)) # => 17.0# Using Int
print(17.0) # => 17.0
print(int(17.0)) # => 17# Using Str
print(str(17.0) + ' and ' + str(17)) # => 17.0 and 17print('''My instructions are very long so to make them
more readable in the code I am putting them on
more than one line. I can even include "quotes"
of any kind because they won't get confused with
the end of the string!''')print(len(âSpaghettiâ)) # => 9print(âSpaghettiâ[-1]) # => i print(âSpaghettiâ[-4]) # => eprint(âSpaghettiâ[1:4]) # => pag
print(âSpaghettiâ[4:-1]) # => hett
print(âSpaghettiâ[4:4]) # => (empty string)# Shortcut to get from the beginning of a string to a certain index.
print("Spaghetti"[:4]) # => Spag
print("Spaghetti"[:-1]) # => Spaghett# Shortcut to get from a certain index to the end of a string.
print("Spaghetti"[1:]) # => paghetti
print("Spaghetti"[-4:]) # => ettiprint("Spaghetti".index("h")) # => 4
print("Spaghetti".index("t")) # => 6print("Spaghetti".count("h")) # => 1
print("Spaghetti".count("t")) # => 2
print("Spaghetti".count("s")) # => 0
print('''We choose to go to the moon in this decade and do the other things,
not because they are easy, but because they are hard, because that goal will
serve to organize and measure the best of our energies and skills, because that
challenge is one that we are willing to accept, one we are unwilling to
postpone, and one which we intend to win, and the others, too.
'''.count('the ')) # => 4first_name = "Billy"
last_name = "Bob"
print('Your name is {0} {1}'.format(first_name, last_name)) # => Your name is Billy Boba = 7
b = 'Marbles'
print(a) # => 7
print(b) # => Marblescount = max = min = 0
print(count) # => 0
print(max) # => 0
print(min) # => 0a = 17
print(a) # => 17
a = 'seventeen'
print(a) # => seventeen# Logical AND
print(True and True) # => True
print(True and False) # => False
print(False and False) # => False# Logical OR
print(True or True) # => True
print(True or False) # => True
print(False or False) # => False# Logical NOT
print(not True) # => False
print(not False and True) # => True
print(not True or False) # => Falseprint (2 == '2') # => False
print (2 is '2') # => Falseprint ("2" == '2') # => True
print ("2" is '2') # => True# There is a distinction between the number types.
print (2 == 2.0) # => True
print (2 is 2.0) # => Falsespam = 0
while spam < 5:
print('Hello, world.')
spam = spam + 1spam = 0
while True:
print('Hello, world.')
spam = spam + 1
if spam >= 5:
breakspam = 0
while True:
print('Hello, world.')
spam = spam + 1
if spam < 5:
continue
breaka = 321
try:
print(len(a))
except:
print('Silently handle error here') # Optionally include a correction to the issue
a = str(a)
print(len(a)a = '321'
try:
print(len(a))
except:
print('Silently handle error here') # Optionally include a correction to the issue
a = str(a)
print(len(a))a = 100
b = 0
try:
c = a / b
except ZeroDivisionError:
c = None
print(c)a = 100
b = 0
try:
print(a / b)
except ZeroDivisionError:
passa = 100
# b = "5"
try:
print(a / b)
except ZeroDivisionError:
pass
except (TypeError, NameError):
print("ERROR!")# tuple of file names
files = ('one.txt', 'two.txt', 'three.txt')# simple loop
for filename in files:
try:
# open the file in read mode
f = open(filename, 'r')
except OSError:
# handle the case where file does not exist or permission is denied
print('cannot open file', filename)
else:
# do stuff with the file object (f)
print(filename, 'opened successfully')
print('found', len(f.readlines()), 'lines')
f.close()def divide(x, y):
try:
result = x / y
except ZeroDivisionError:
print("Cannot divide by zero")
else:
print("Result is", result)
finally:
print("Finally...")# Try a number - nothing will print out
a = 321
if hasattr(a, '__len__'):
print(len(a))# Try a string - the length will print out (4 in this case)
b = "5555"
if hasattr(b, '__len__'):
print(len(b))if (true) {
}while (true) {}if True:
passwhile True:
passdef greeting(name, saying="Hello"):
print(saying, name)greeting("Monica")
# Hello Monicagreeting("Barry", "Hey")
# Hey Barry# THIS IS BAD CODE AND WILL NOT RUN
def increment(delta=1, value):
return delta + valuedef greeting(name, saying="Hello"):
print(saying, name)# name has no default value, so just provide the value
# saying has a default value, so use a keyword argument
greeting("Monica", saying="Hi")shopping_list = [âbreadâ,âmilkâ,âeggsâ]
print(â,â.join(shopping_list))print(â{:,}â.format(1234567890))
â1,234,567,890âd = datetime.datetime(2020, 7, 4, 12, 15, 58)
print(â{:%Y-%m-%d %H:%M:%S}â.format(d))
â2020â07â04 12:15:58âpoints = 190
total = 220
print(âCorrect answers: {:.2%}â.format(points/total))
Correct answers: 86.36%width=8
print(â decimal hex binaryâ)
print(â-â*27)
for num in range(1,16):
for base in âdXbâ:
print(â{0:{width}{base}}â.format(num, base=base, width=width), end=â â)
print()
Getting Input from the Command Line
Python runs synchronously, all programs and processes will stop when listening for a user input.
The input function shows a prompt to a user and waits for them to type âENTERâ.
Scripts vs Programs
Programming Script : A set of code that runs in a linear fashion.
The largest difference between scripts and programs is the level of complexity and purpose. Programs typically have many UIâs.empty_list = []
departments = [âHRâ,âDevelopmentâ,âSalesâ,âFinanceâ,âITâ,âCustomer Supportâ]specials = list()print(1 in [1, 2, 3]) #> True
print(4 in [1, 2, 3]) #> False
# Tuples : Very similar to lists, but they are immutabletime_blocks = (âAMâ,âPMâ)colors = âredâ,âblueâ,âgreenâ
numbers = 1, 2, 3tuple(âabcâ) # returns (âaâ, âbâ, âcâ)
tuple([1,2,3]) # returns (1, 2, 3)
# Think of tuples as constant variables.range(5) # [0, 1, 2, 3, 4]
range(1,5) # [1, 2, 3, 4]
range(0, 25, 5) # [0, 5, 10, 15, 20]
range(0) # [ ]
for let (i = 0; i < 5; i++)
for let (i = 1; i < 5; i++)
for let (i = 0; i < 25; i+=5)
for let(i = 0; i = 0; i++)
# Keep in mind that stop is not included in the range.a = {âoneâ:1, âtwoâ:2, âthreeâ:3}
b = dict(one=1, two=2, three=3)
c = dict([(âtwoâ, 2), (âoneâ, 1), (âthreeâ, 3)])
# a, b, and c are all equalschool_bag = {âbookâ,âpaperâ,âpencilâ,âpencilâ,âbookâ,âbookâ,âbookâ,âeraserâ}
print(school_bag)letters = set(âabracadabraâ)
print(letters)
#Built-In Functions
#Functions using iterablesquarters = [âFirstâ, âSecondâ, âThirdâ, âFourthâ]
print(enumerate(quarters))
print(enumerate(quarters, start=1))a = {1, 2, 3}
b = {2, 4, 6}
print(a | b) # => {1, 2, 3, 4, 6}
a = {1, 2, 3}
b = {2, 4, 6}
print(a & b) # => {2}
Difference : The â operator can be used to produce a new set of only the elements that appear in the first set and NOT the others.a = {1, 2, 3}
b = {2, 4, 6}
print(a â b) # => {1, 3}
print(b â a) # => {4, 6}
print(a ^ b) # => {1, 3, 4, 6}print(âMy name isâ)
for i in range(5):
print(âCarlita Cinco (â + str(i) + â)â)total = 0
for num in range(101):
total += num
print(total)
Looping over a list in Python
for c in [âaâ, âbâ, âcâ]:
print(c)lst = [0, 1, 2, 3]
for i in lst:
print(i)supplies = [âpensâ, âstaplersâ, âflame-throwersâ, âbindersâ]
for i in range(len(supplies)):
print(âIndex â + str(i) + â in supplies is: â + supplies[i])
l = 1, 2], [3, 4], [5, 6
for a, b in l:
print(a, â, â, b)spam = {âcolorâ: âredâ, âageâ: 42}
for v in spam.values():
print(v)for k in spam.keys():
print(k)for i in spam.items():
print(i)for k, v in spam.items():
print(âKey: â + k + â Value: â + str(v))for c in âabcdefgâ:
print(c)def example(arg_1, arg_2, *args, **kwargs):
passdef example2(arg_1, arg_2, *args, kw_1=âsharkâ, kw_2=âblowfishâ, **kwargs):
pass
from urllib.request import (
HTTPDefaultErrorHandler as ErrorHandler,
HTTPRedirectHandler as RedirectHandler,
Request,
pathname2url,
url2pathname,
urlopen,
)***and del for is raiseassert elif from lambda returnbreak else global not tryclass except if or whilecontinue exec import passdef finally in print*** `def perm(l): # error: first line indented
for i in range(len(l)): # error: not indented
s = l[:i] + l[i+1:]
p = perm(l[:i] + l[i+1:]) # error: unexpected indent
for x in p:
r.append(l[i:i+1] + x)
return r # error: inconsistent dedent`def foo():
"""
The foo function does many amazing things that you
should not question. Just accept that it exists and
use it with caution.
"""
secretThing()print(3) # => 3
print(int(19)) # => 19
print(int()) # => 0print(2.24) # => 2.24
print(2.) # => 2.0
print(float()) # => 0.0
print(27e-5) # => 0.00027print(7j) # => 7j
print(5.1+7.7j)) # => 5.1+7.7j
print(complex(3, 5)) # => 3+5j
print(complex(17)) # => 17+0j
print(complex()) # => 0j# Using Float
print(17) # => 17
print(float(17)) # => 17.0# Using Int
print(17.0) # => 17.0
print(int(17.0)) # => 17# Using Str
print(str(17.0) + ' and ' + str(17)) # => 17.0 and 17print('''My instructions are very long so to make them
more readable in the code I am putting them on
more than one line. I can even include "quotes"
of any kind because they won't get confused with
the end of the string!''')print(len(âSpaghettiâ)) # => 9print(âSpaghettiâ[-1]) # => i print(âSpaghettiâ[-4]) # => eprint(âSpaghettiâ[1:4]) # => pag
print(âSpaghettiâ[4:-1]) # => hett
print(âSpaghettiâ[4:4]) # => (empty string)# Shortcut to get from the beginning of a string to a certain index.
print("Spaghetti"[:4]) # => Spag
print("Spaghetti"[:-1]) # => Spaghett# Shortcut to get from a certain index to the end of a string.
print("Spaghetti"[1:]) # => paghetti
print("Spaghetti"[-4:]) # => ettiprint("Spaghetti".index("h")) # => 4
print("Spaghetti".index("t")) # => 6print("Spaghetti".count("h")) # => 1
print("Spaghetti".count("t")) # => 2
print("Spaghetti".count("s")) # => 0
print('''We choose to go to the moon in this decade and do the other things,
not because they are easy, but because they are hard, because that goal will
serve to organize and measure the best of our energies and skills, because that
challenge is one that we are willing to accept, one we are unwilling to
postpone, and one which we intend to win, and the others, too.
'''.count('the ')) # => 4first_name = "Billy"
last_name = "Bob"
print('Your name is {0} {1}'.format(first_name, last_name)) # => Your name is Billy Boba = 7
b = 'Marbles'
print(a) # => 7
print(b) # => Marblescount = max = min = 0
print(count) # => 0
print(max) # => 0
print(min) # => 0a = 17
print(a) # => 17
a = 'seventeen'
print(a) # => seventeen# Logical AND
print(True and True) # => True
print(True and False) # => False
print(False and False) # => False# Logical OR
print(True or True) # => True
print(True or False) # => True
print(False or False) # => False# Logical NOT
print(not True) # => False
print(not False and True) # => True
print(not True or False) # => Falseprint (2 == '2') # => False
print (2 is '2') # => Falseprint ("2" == '2') # => True
print ("2" is '2') # => True# There is a distinction between the number types.
print (2 == 2.0) # => True
print (2 is 2.0) # => Falsespam = 0
while spam < 5:
print('Hello, world.')
spam = spam + 1spam = 0
while True:
print('Hello, world.')
spam = spam + 1
if spam >= 5:
breakspam = 0
while True:
print('Hello, world.')
spam = spam + 1
if spam < 5:
continue
breaka = 321
try:
print(len(a))
except:
print('Silently handle error here') # Optionally include a correction to the issue
a = str(a)
print(len(a)a = '321'
try:
print(len(a))
except:
print('Silently handle error here') # Optionally include a correction to the issue
a = str(a)
print(len(a))a = 100
b = 0
try:
c = a / b
except ZeroDivisionError:
c = None
print(c)a = 100
b = 0
try:
print(a / b)
except ZeroDivisionError:
passa = 100
# b = "5"
try:
print(a / b)
except ZeroDivisionError:
pass
except (TypeError, NameError):
print("ERROR!")# tuple of file names
files = ('one.txt', 'two.txt', 'three.txt')# simple loop
for filename in files:
try:
# open the file in read mode
f = open(filename, 'r')
except OSError:
# handle the case where file does not exist or permission is denied
print('cannot open file', filename)
else:
# do stuff with the file object (f)
print(filename, 'opened successfully')
print('found', len(f.readlines()), 'lines')
f.close()def divide(x, y):
try:
result = x / y
except ZeroDivisionError:
print("Cannot divide by zero")
else:
print("Result is", result)
finally:
print("Finally...")# Try a number - nothing will print out
a = 321
if hasattr(a, '__len__'):
print(len(a))# Try a string - the length will print out (4 in this case)
b = "5555"
if hasattr(b, '__len__'):
print(len(b))if (true) {
}while (true) {}if True:
passwhile True:
passdef greeting(name, saying="Hello"):
print(saying, name)greeting("Monica")
# Hello Monicagreeting("Barry", "Hey")
# Hey Barry# THIS IS BAD CODE AND WILL NOT RUN
def increment(delta=1, value):
return delta + valuedef greeting(name, saying="Hello"):
print(saying, name)# name has no default value, so just provide the value
# saying has a default value, so use a keyword argument
greeting("Monica", saying="Hi")shopping_list = [âbreadâ,âmilkâ,âeggsâ]
print(â,â.join(shopping_list))print(â{:,}â.format(1234567890))
â1,234,567,890âd = datetime.datetime(2020, 7, 4, 12, 15, 58)
print(â{:%Y-%m-%d %H:%M:%S}â.format(d))
â2020â07â04 12:15:58âpoints = 190
total = 220
print(âCorrect answers: {:.2%}â.format(points/total))
Correct answers: 86.36%width=8
print(â decimal hex binaryâ)
print(â-â*27)
for num in range(1,16):
for base in âdXbâ:
print(â{0:{width}{base}}â.format(num, base=base, width=width), end=â â)
print()
Getting Input from the Command Line
Python runs synchronously, all programs and processes will stop when listening for a user input.
The input function shows a prompt to a user and waits for them to type âENTERâ.
Scripts vs Programs
Programming Script : A set of code that runs in a linear fashion.
The largest difference between scripts and programs is the level of complexity and purpose. Programs typically have many UIâs.empty_list = []
departments = [âHRâ,âDevelopmentâ,âSalesâ,âFinanceâ,âITâ,âCustomer Supportâ]specials = list()print(1 in [1, 2, 3]) #> True
print(4 in [1, 2, 3]) #> False
# Tuples : Very similar to lists, but they are immutabletime_blocks = (âAMâ,âPMâ)colors = âredâ,âblueâ,âgreenâ
numbers = 1, 2, 3tuple(âabcâ) # returns (âaâ, âbâ, âcâ)
tuple([1,2,3]) # returns (1, 2, 3)
# Think of tuples as constant variables.range(5) # [0, 1, 2, 3, 4]
range(1,5) # [1, 2, 3, 4]
range(0, 25, 5) # [0, 5, 10, 15, 20]
range(0) # [ ]
for let (i = 0; i < 5; i++)
for let (i = 1; i < 5; i++)
for let (i = 0; i < 25; i+=5)
for let(i = 0; i = 0; i++)
# Keep in mind that stop is not included in the range.a = {âoneâ:1, âtwoâ:2, âthreeâ:3}
b = dict(one=1, two=2, three=3)
c = dict([(âtwoâ, 2), (âoneâ, 1), (âthreeâ, 3)])
# a, b, and c are all equalschool_bag = {âbookâ,âpaperâ,âpencilâ,âpencilâ,âbookâ,âbookâ,âbookâ,âeraserâ}
print(school_bag)letters = set(âabracadabraâ)
print(letters)
#Built-In Functions
#Functions using iterablesquarters = [âFirstâ, âSecondâ, âThirdâ, âFourthâ]
print(enumerate(quarters))
print(enumerate(quarters, start=1))a = {1, 2, 3}
b = {2, 4, 6}
print(a | b) # => {1, 2, 3, 4, 6}
a = {1, 2, 3}
b = {2, 4, 6}
print(a & b) # => {2}
Difference : The â operator can be used to produce a new set of only the elements that appear in the first set and NOT the others.a = {1, 2, 3}
b = {2, 4, 6}
print(a â b) # => {1, 3}
print(b â a) # => {4, 6}
print(a ^ b) # => {1, 3, 4, 6}print(âMy name isâ)
for i in range(5):
print(âCarlita Cinco (â + str(i) + â)â)total = 0
for num in range(101):
total += num
print(total)
Looping over a list in Python
for c in [âaâ, âbâ, âcâ]:
print(c)lst = [0, 1, 2, 3]
for i in lst:
print(i)supplies = [âpensâ, âstaplersâ, âflame-throwersâ, âbindersâ]
for i in range(len(supplies)):
print(âIndex â + str(i) + â in supplies is: â + supplies[i])
l = 1, 2], [3, 4], [5, 6
for a, b in l:
print(a, â, â, b)spam = {âcolorâ: âredâ, âageâ: 42}
for v in spam.values():
print(v)for k in spam.keys():
print(k)for i in spam.items():
print(i)for k, v in spam.items():
print(âKey: â + k + â Value: â + str(v))for c in âabcdefgâ:
print(c)def example(arg_1, arg_2, *args, **kwargs):
passdef example2(arg_1, arg_2, *args, kw_1=âsharkâ, kw_2=âblowfishâ, **kwargs):
pass
from urllib.request import (
HTTPDefaultErrorHandler as ErrorHandler,
HTTPRedirectHandler as RedirectHandler,
Request,
pathname2url,
url2pathname,
urlopen,
)
