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About

Basic cheatsheet for Python mostly based on the book written by Al Sweigart, Automate the Boring Stuff with Python under the Creative Commons license and many other sources.

Contribute

All contributions are welcome:

• Read the issues, Fork the project and do a Pull Request.
• Request a new topic creating a New issue with the enhancement tag.
• Find any kind of errors in the cheat sheet and create a New issue with the details or fork the project and do a Pull Request.
• Suggest a better or more pythonic way for existing examples.

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Python Cheatsheet

• About
  • Contribute
  • Read It
  • Python Cheatsheet
  • The Zen of Python
  • Python Basics
    • Math Operators
    • Data Types
    • String Concatenation and Replication
    • Variables
    • Comments
    • The print() Function
    • The input() Function
    • The len() Function
    • The str(), int(), and float() Functions
  • Flow Control
    • Comparison Operators
    • Boolean evaluation
    • Boolean Operators
    • Mixing Boolean and Comparison Operators
    • if Statements
    • else Statements
    • elif Statements
    • while Loop Statements
    • break Statements
    • continue Statements
    • for Loops and the range() Function
    • For else statement
    • Importing Modules
    • Ending a Program Early with sys.exit()
  • Functions
    • Return Values and return Statements
    • The None Value
    • Keyword Arguments and print()
    • Local and Global Scope
    • The global Statement
  • Exception Handling
    • Basic exception handling
    • Final code in exception handling
  • Lists
    • Getting Individual Values in a List with Indexes
    • Negative Indexes
    • Getting Sublists with Slices
    • Getting a List’s Length with len()
    • Changing Values in a List with Indexes
    • List Concatenation and List Replication
    • Removing Values from Lists with del Statements
    • Using for Loops with Lists
    • Looping Through Multiple Lists with zip()
    • The in and not in Operators
    • The Multiple Assignment Trick
    • Augmented Assignment Operators
    • Finding a Value in a List with the index() Method
    • Adding Values to Lists with the append() and insert() Methods
    • Removing Values from Lists with remove()
    • Removing Values from Lists with pop()
    • Sorting the Values in a List with the sort() Method
    • Tuple Data Type
    • Converting Types with the list() and tuple() Functions
  • Dictionaries and Structuring Data
    • The keys(), values(), and items() Methods
    • Checking Whether a Key or Value Exists in a Dictionary
    • The get() Method
    • The setdefault() Method
    • Pretty Printing
    • Merge two dictionaries
  • sets
    • Initializing a set
    • sets: unordered collections of unique elements
    • set add() and update()
    • set remove() and discard()
    • set union()
    • set intersection
    • set difference
    • set symetric_difference
  • itertools Module
    • accumulate()
    • combinations()
    • combinations_with_replacement()
    • count()
    • cycle()
    • chain()
    • compress()
    • dropwhile()
    • filterfalse()
    • groupby()
    • islice()
    • permutations()
    • product()
    • repeat()
    • starmap()
    • takewhile()
    • tee()
    • zip_longest()
  • Comprehensions
    • List comprehension
    • Set comprehension
    • Dict comprehension
  • Manipulating Strings
    • Escape Characters
    • Raw Strings
    • Multiline Strings with Triple Quotes
    • Indexing and Slicing Strings
    • The in and not in Operators with Strings
    • The in and not in Operators with list
    • The upper(), lower(), isupper(), and islower() String Methods
    • The isX String Methods
    • The startswith() and endswith() String Methods
    • The join() and split() String Methods
    • Justifying Text with rjust(), ljust(), and center()
    • Removing Whitespace with strip(), rstrip(), and lstrip()
    • Copying and Pasting Strings with the pyperclip Module (need pip install)
  • String Formatting
    • % operator
    • String Formatting (str.format)
    • Lazy string formatting
    • Formatted String Literals or f-strings (Python 3.6+)
    • Template Strings
  • Regular Expressions
    • Matching Regex Objects
    • Grouping with Parentheses
    • Matching Multiple Groups with the Pipe
    • Optional Matching with the Question Mark
    • Matching Zero or More with the Star
    • Matching One or More with the Plus
    • Matching Specific Repetitions with Curly Brackets
    • Greedy and Nongreedy Matching
    • The findall() Method
    • Making Your Own Character Classes
    • The Caret and Dollar Sign Characters
    • The Wildcard Character
    • Matching Everything with Dot-Star
    • Matching Newlines with the Dot Character
    • Review of Regex Symbols
    • Case-Insensitive Matching
    • Substituting Strings with the sub() Method
    • Managing Complex Regexes
  • Handling File and Directory Paths
    • Backslash on Windows and Forward Slash on OS X and Linux
    • The Current Working Directory
    • Creating New Folders
    • Absolute vs. Relative Paths
    • Handling Absolute and Relative Paths
    • Checking Path Validity
    • Finding File Sizes and Folder Contents
    • Copying Files and Folders
    • Moving and Renaming Files and Folders
    • Permanently Deleting Files and Folders
    • Safe Deletes with the send2trash Module
    • Walking a Directory Tree
  • Reading and Writing Files
    • The File Reading/Writing Process
    • Opening and reading files with the open() function
    • Writing to Files
    • Saving Variables with the shelve Module
    • Saving Variables with the pprint.pformat() Function
    • Reading ZIP Files
    • Extracting from ZIP Files
    • Creating and Adding to ZIP Files
  • JSON, YAML and configuration files
    • JSON
    • YAML
    • Anyconfig
  • Debugging
    • Raising Exceptions
    • Getting the Traceback as a String
    • Assertions
    • Logging
    • Logging Levels
    • Disabling Logging
    • Logging to a File
  • Lambda Functions
  • Ternary Conditional Operator
  • args and kwargs
    • Things to Remember(args)
    • Things to Remember(kwargs)
  • Context Manager
    • with statement
    • Writing your own contextmanager using generator syntax
  • __main__ Top-level script environment
    • Advantages
  • setup.py
  • Dataclasses
    • Features
    • Default values
    • Type hints
  • Virtual Environment
    • virtualenv
    • poetry
    • pipenv
    • anaconda

The Zen of Python

From the PEP 20 -- The Zen of Python:

Long time Pythoneer Tim Peters succinctly channels the BDFL's guiding principles for Python's design into 20 aphorisms, only 19 of which have been written down.

>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

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Python Basics

Math Operators

From Highest to Lowest precedence:

Examples of expressions in the interactive shell:

>>> 2 + 3 * 6
20

>>> (2 + 3) * 6
30

>>> 2 ** 8
256

>>> 23 // 7
3

>>> 23 % 7
2

>>> (5 - 1) * ((7 + 1) / (3 - 1))
16.0

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Data Types

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String Concatenation and Replication

String concatenation:

>>> 'Alice' 'Bob'
'AliceBob'

Note: Avoid + operator for string concatenation. Prefer string formatting.

String Replication:

>>> 'Alice' * 5
'AliceAliceAliceAliceAlice'

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Variables

You can name a variable anything as long as it obeys the following rules:

1. It can be only one word.
2. It can use only letters, numbers, and the underscore (_) character.
3. It can’t begin with a number.
4. Variable name starting with an underscore (_) are considered as "unuseful`.

Example:

>>> spam = 'Hello'
>>> spam
'Hello'

>>> _spam = 'Hello'

_spam should not be used again in the code.

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Comments

Inline comment:

# This is a comment

Multiline comment:

# This is a
# multiline comment

Code with a comment:

a = 1  # initialization

Please note the two spaces in front of the comment.

Function docstring:

def foo():
    """
    This is a function docstring
    You can also use:
    ''' Function Docstring '''
    """

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The print() Function

>>> print('Hello world!')
Hello world!

>>> a = 1
>>> print('Hello world!', a)
Hello world! 1

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The input() Function

Example Code:

>>> print('What is your name?')   # ask for their name
>>> myName = input()
>>> print('It is good to meet you, {}'.format(myName))
What is your name?
Al
It is good to meet you, Al

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The len() Function

Evaluates to the integer value of the number of characters in a string:

>>> len('hello')
5

Note: test of emptiness of strings, lists, dictionary, etc, should not use len, but prefer direct boolean evaluation.

>>> a = [1, 2, 3]
>>> if a:
>>>     print("the list is not empty!")

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The str(), int(), and float() Functions

Integer to String or Float:

>>> str(29)
'29'

>>> print('I am {} years old.'.format(str(29)))
I am 29 years old.

>>> str(-3.14)
'-3.14'

Float to Integer:

>>> int(7.7)
7

>>> int(7.7) + 1
8

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Flow Control

Comparison Operators

These operators evaluate to True or False depending on the values you give them.

Examples:

>>> 42 == 42
True

>>> 40 == 42
False

>>> 'hello' == 'hello'
True

>>> 'hello' == 'Hello'
False

>>> 'dog' != 'cat'
True

>>> 42 == 42.0
True

>>> 42 == '42'
False

Boolean evaluation

Never use == or != operator to evaluate boolean operation. Use the is or is not operators, or use implicit boolean evaluation.

NO (even if they are valid Python):

>>> True == True
True

>>> True != False
True

YES (even if they are valid Python):

>>> True is True
True

>>> True is not False
True

These statements are equivalent:

>>> if a is True:
>>>    pass
>>> if a is not False:
>>>    pass
>>> if a:
>>>    pass

And these as well:

>>> if a is False:
>>>    pass
>>> if a is not True:
>>>    pass
>>> if not a:
>>>    pass

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Boolean Operators

There are three Boolean operators: and, or, and not.

The and Operator’s Truth Table:

The or Operator’s Truth Table:

The not Operator’s Truth Table:

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Mixing Boolean and Comparison Operators

>>> (4 < 5) and (5 < 6)
True

>>> (4 < 5) and (9 < 6)
False

>>> (1 == 2) or (2 == 2)
True

You can also use multiple Boolean operators in an expression, along with the comparison operators:

>>> 2 + 2 == 4 and not 2 + 2 == 5 and 2 * 2 == 2 + 2
True

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if Statements

if name == 'Alice':
    print('Hi, Alice.')

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else Statements

name = 'Bob'
if name == 'Alice':
    print('Hi, Alice.')
else:
    print('Hello, stranger.')

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elif Statements

name