Python (programming language)

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Python (programming language)_table_infobox_0

PythonPython (programming language)_table_caption_0
ParadigmPython (programming language)_header_cell_0_0_0 Multi-paradigm: functional, imperative, object-oriented, structured, reflectivePython (programming language)_cell_0_0_1
Designed byPython (programming language)_header_cell_0_1_0 Guido van RossumPython (programming language)_cell_0_1_1
DeveloperPython (programming language)_header_cell_0_2_0 Python Software FoundationPython (programming language)_cell_0_2_1
First appearedPython (programming language)_header_cell_0_3_0 1991; 29 years ago (1991)Python (programming language)_cell_0_3_1
Stable releasePython (programming language)_header_cell_0_4_0 3.9.1
  / 7 December 2020; 6 days ago (2020-12-07)Python (programming language)_cell_0_4_1
Preview releasePython (programming language)_header_cell_0_5_0 3.10.0a3
  / 7 December 2020; 6 days ago (2020-12-07)Python (programming language)_cell_0_5_1
Typing disciplinePython (programming language)_header_cell_0_6_0 Duck, dynamic, gradual (since 3.5)Python (programming language)_cell_0_6_1
OSPython (programming language)_header_cell_0_7_0 Linux, macOS, Windows 8 and later
and morePython (programming language)_cell_0_7_1
LicensePython (programming language)_header_cell_0_8_0 Python Software Foundation LicensePython (programming language)_cell_0_8_1
Python (programming language)_header_cell_0_9_0 .py, .pyi, .pyc, .pyd, .pyo (prior to 3.5), .pyw, .pyz (since 3.5)Python (programming language)_cell_0_9_1
WebsitePython (programming language)_header_cell_0_10_0 Python (programming language)_cell_0_10_1
Major implementationsPython (programming language)_header_cell_0_11_0
DialectsPython (programming language)_header_cell_0_12_0
Influenced byPython (programming language)_header_cell_0_13_0
InfluencedPython (programming language)_header_cell_0_14_0

Python is an interpreted, high-level and general-purpose programming language. Python (programming language)_sentence_0

Python's design philosophy emphasizes code readability with its notable use of significant whitespace. Python (programming language)_sentence_1

Its language constructs and object-oriented approach aim to help programmers write clear, logical code for small and large-scale projects. Python (programming language)_sentence_2

Python is dynamically typed and garbage-collected. Python (programming language)_sentence_3

It supports multiple programming paradigms, including structured (particularly, procedural), object-oriented, and functional programming. Python (programming language)_sentence_4

Python is often described as a "batteries included" language due to its comprehensive standard library. Python (programming language)_sentence_5

Python was created in the late 1980s, and first released in 1991, by Guido van Rossum as a successor to the ABC programming language. Python (programming language)_sentence_6

Python 2.0, released in 2000, introduced new features, such as list comprehensions, and a garbage collection system with reference counting, and was discontinued with version 2.7 in 2020. Python (programming language)_sentence_7

Python 3.0, released in 2008, was a major revision of the language that is not completely backward-compatible and much Python 2 code does not run unmodified on Python 3. Python (programming language)_sentence_8

With Python 2's end-of-life, only Python 3.6.x and later are supported, with older versions still supporting e.g. Windows 7 (and old installers not restricted to 64-bit Windows). Python (programming language)_sentence_9

Python interpreters are supported for mainstream operating systems and available for a few more (and in the past supported many more). Python (programming language)_sentence_10

A global community of programmers develops and maintains CPython, a free and open-source reference implementation. Python (programming language)_sentence_11

A non-profit organization, the Python Software Foundation, manages and directs resources for Python and CPython development. Python (programming language)_sentence_12

It currently ties with Java as the second most popular programming language in the world. Python (programming language)_sentence_13

History Python (programming language)_section_0

Main article: History of Python Python (programming language)_sentence_14

Python was conceived in the late 1980s by Guido van Rossum at Centrum Wiskunde & Informatica (CWI) in the Netherlands as a successor to the ABC programming language, which was inspired by SETL), capable of exception handling and interfacing with the Amoeba operating system. Python (programming language)_sentence_15

Its implementation began in December 1989. Python (programming language)_sentence_16

Van Rossum shouldered sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his "permanent vacation" from his responsibilities as Python's Benevolent Dictator For Life, a title the Python community bestowed upon him to reflect his long-term commitment as the project's chief decision-maker. Python (programming language)_sentence_17

He now shares his leadership as a member of a five-person steering council. Python (programming language)_sentence_18

In January 2019, active Python core developers elected Brett Cannon, Nick Coghlan, Barry Warsaw, Carol Willing and Van Rossum to a five-member "Steering Council" to lead the project. Python (programming language)_sentence_19

Guido van Rossum has since then withdrawn his nomination for the 2020 Steering council. Python (programming language)_sentence_20

Python 2.0 was released on 16 October 2000 with many major new features, including a cycle-detecting garbage collector and support for Unicode. Python (programming language)_sentence_21

Python 3.0 was released on 3 December 2008. Python (programming language)_sentence_22

It was a major revision of the language that is not completely backward-compatible. Python (programming language)_sentence_23

Many of its major features were backported to Python 2.6.x and 2.7.x version series. Python (programming language)_sentence_24

Releases of Python 3 include the 2to3 utility, which automates (at least partially) the translation of Python 2 code to Python 3. Python (programming language)_sentence_25

Python 2.7's end-of-life date was initially set at 2015 then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3. Python (programming language)_sentence_26

No more security patches or other improvements will be released for it. Python (programming language)_sentence_27

With Python 2's end-of-life, only Python 3.6.x and later are supported. Python (programming language)_sentence_28

Design philosophy and features Python (programming language)_section_1

Python is a multi-paradigm programming language. Python (programming language)_sentence_29

Object-oriented programming and structured programming are fully supported, and many of its features support functional programming and aspect-oriented programming (including by metaprogramming and metaobjects (magic methods)). Python (programming language)_sentence_30

Many other paradigms are supported via extensions, including design by contract and logic programming. Python (programming language)_sentence_31

Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management. Python (programming language)_sentence_32

It also features dynamic name resolution (late binding), which binds method and variable names during program execution. Python (programming language)_sentence_33

Python's design offers some support for functional programming in the Lisp tradition. Python (programming language)_sentence_34

It has filter, map, and reduce functions; list comprehensions, dictionaries, sets, and generator expressions. Python (programming language)_sentence_35

The standard library has two modules (itertools and functools) that implement functional tools borrowed from Haskell and Standard ML. Python (programming language)_sentence_36

The language's core philosophy is summarized in the document The Zen of Python (PEP 20), which includes aphorisms such as: Python (programming language)_sentence_37

Python (programming language)_unordered_list_0

  • Beautiful is better than ugly.Python (programming language)_item_0_0
  • Explicit is better than implicit.Python (programming language)_item_0_1
  • Simple is better than complex.Python (programming language)_item_0_2
  • Complex is better than complicated.Python (programming language)_item_0_3
  • Readability counts.Python (programming language)_item_0_4

Rather than having all of its functionality built into its core, Python was designed to be highly extensible. Python (programming language)_sentence_38

This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. Python (programming language)_sentence_39

Van Rossum's vision of a small core language with a large standard library and easily extensible interpreter stemmed from his frustrations with ABC, which espoused the opposite approach. Python (programming language)_sentence_40

Python strives for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. Python (programming language)_sentence_41

In contrast to Perl's "there is more than one way to do it" motto, Python embraces a "there should be one—and preferably only one—obvious way to do it" design philosophy. Python (programming language)_sentence_42

Alex Martelli, a Fellow at the Python Software Foundation and Python book author, writes that "To describe something as 'clever' is not considered a compliment in the Python culture." Python (programming language)_sentence_43

Python's developers strive to avoid premature optimization, and reject patches to non-critical parts of the CPython reference implementation that would offer marginal increases in speed at the cost of clarity. Python (programming language)_sentence_44

When speed is important, a Python programmer can move time-critical functions to extension modules written in languages such as C, or use PyPy, a just-in-time compiler. Python (programming language)_sentence_45

Cython is also available, which translates a Python script into C and makes direct C-level API calls into the Python interpreter. Python (programming language)_sentence_46

An important goal of Python's developers is keeping it fun to use. Python (programming language)_sentence_47

This is reflected in the language's name—a tribute to the British comedy group Monty Python—and in occasionally playful approaches to tutorials and reference materials, such as examples that refer to spam and eggs (from a famous Monty Python sketch) instead of the standard foo and bar. Python (programming language)_sentence_48

A common neologism in the Python community is pythonic, which can have a wide range of meanings related to program style. Python (programming language)_sentence_49

To say that code is pythonic is to say that it uses Python idioms well, that it is natural or shows fluency in the language, that it conforms with Python's minimalist philosophy and emphasis on readability. Python (programming language)_sentence_50

In contrast, code that is difficult to understand or reads like a rough transcription from another programming language is called unpythonic. Python (programming language)_sentence_51

Users and admirers of Python, especially those considered knowledgeable or experienced, are often referred to as Pythonistas. Python (programming language)_sentence_52

Syntax and semantics Python (programming language)_section_2

Main article: Python syntax and semantics Python (programming language)_sentence_53

Python is meant to be an easily readable language. Python (programming language)_sentence_54

Its formatting is visually uncluttered, and it often uses English keywords where other languages use punctuation. Python (programming language)_sentence_55

Unlike many other languages, it does not use curly brackets to delimit blocks, and semicolons after statements are optional. Python (programming language)_sentence_56

It has fewer syntactic exceptions and special cases than C or Pascal. Python (programming language)_sentence_57

Indentation Python (programming language)_section_3

Main article: Python syntax and semantics § Indentation Python (programming language)_sentence_58

Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. Python (programming language)_sentence_59

An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block. Python (programming language)_sentence_60

Thus, the program's visual structure accurately represents the program's semantic structure. Python (programming language)_sentence_61

This feature is sometimes termed the off-side rule, which some other languages share, but in most languages indentation doesn't have any semantic meaning. Python (programming language)_sentence_62

Statements and control flow Python (programming language)_section_4

Python's statements include (among others): Python (programming language)_sentence_63

Python (programming language)_unordered_list_1

  • The assignment statement (token '=', the equals sign). This operates differently than in traditional imperative programming languages, and this fundamental mechanism (including the nature of Python's version of variables) illuminates many other features of the language. Assignment in C, e.g., x = 2, translates to "typed variable name x receives a copy of numeric value 2". The (right-hand) value is copied into an allocated storage location for which the (left-hand) variable name is the symbolic address. The memory allocated to the variable is large enough (potentially quite large) for the declared type. In the simplest case of Python assignment, using the same example, x = 2, translates to "(generic) name x receives a reference to a separate, dynamically allocated object of numeric (int) type of value 2." This is termed binding the name to the object. Since the name's storage location doesn't contain the indicated value, it is improper to call it a variable. Names may be subsequently rebound at any time to objects of greatly varying types, including strings, procedures, complex objects with data and methods, etc. Successive assignments of a common value to multiple names, e.g., x = 2; y = 2; z = 2 result in allocating storage to (at most) three names and one numeric object, to which all three names are bound. Since a name is a generic reference holder it is unreasonable to associate a fixed data type with it. However at a given time, a name will be bound to some object, which will have a type; thus there is dynamic typing.Python (programming language)_item_1_5
  • The if statement, which conditionally executes a block of code, along with else and elif (a contraction of else-if).Python (programming language)_item_1_6
  • The for statement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block.Python (programming language)_item_1_7
  • The while statement, which executes a block of code as long as its condition is true.Python (programming language)_item_1_8
  • The try statement, which allows exceptions raised in its attached code block to be caught and handled by except clauses; it also ensures that clean-up code in a finally block will always be run regardless of how the block exits.Python (programming language)_item_1_9
  • The raise statement, used to raise a specified exception or re-raise a caught exception.Python (programming language)_item_1_10
  • The class statement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming.Python (programming language)_item_1_11
  • The def statement, which defines a function or method.Python (programming language)_item_1_12
  • The with statement, from Python 2.5 released in September 2006, which encloses a code block within a context manager (for example, acquiring a lock before the block of code is run and releasing the lock afterwards, or opening a and then closing it), allowing Resource Acquisition Is Initialization (RAII)-like behavior and replaces a common try/finally idiom.Python (programming language)_item_1_13
  • The break statement, exits from the loop.Python (programming language)_item_1_14
  • The continue statement, skips this iteration and continues with the next item.Python (programming language)_item_1_15
  • The pass statement, which serves as a NOP. It is syntactically needed to create an empty code block.Python (programming language)_item_1_16
  • The assert statement, used during debugging to check for conditions that ought to apply.Python (programming language)_item_1_17
  • The yield statement, which returns a value from a generator function. From Python 2.5, yield is also an operator. This form is used to implement coroutines.Python (programming language)_item_1_18
  • The return statement, used to return a value from a function.Python (programming language)_item_1_19
  • The import statement, which is used to import modules whose functions or variables can be used in the current program. There are three ways of using import: import <module name> [as <alias>] or from <module name> import * or from <module name> import <definition 1> [as <alias 1>], <definition 2> [as <alias 2>], ....Python (programming language)_item_1_20
  • The print statement was changed to the print() function in Python 3.Python (programming language)_item_1_21

Python does not support tail call optimization or first-class continuations, and, according to Guido van Rossum, it never will. Python (programming language)_sentence_64

However, better support for coroutine-like functionality is provided in 2.5, by extending Python's generators. Python (programming language)_sentence_65

Before 2.5, generators were lazy iterators; information was passed unidirectionally out of the generator. Python (programming language)_sentence_66

From Python 2.5, it is possible to pass information back into a generator function, and from Python 3.3, the information can be passed through multiple stack levels. Python (programming language)_sentence_67

Expressions Python (programming language)_section_5

Some Python expressions are similar to languages such as C and Java, while some are not: Python (programming language)_sentence_68

Python (programming language)_unordered_list_2

  • Addition, subtraction, and multiplication are the same, but the behavior of division differs. There are two types of divisions in Python. They are floor division (or integer division) // and floating point/division. Python also added the ** operator for exponentiation.Python (programming language)_item_2_22
  • From Python 3.5, the new @ infix operator was introduced. It is intended to be used by libraries such as NumPy for matrix multiplication.Python (programming language)_item_2_23
  • From Python 3.8, the syntax :=, called the 'walrus operator' was introduced. It assigns values to variables as part of a larger expression.Python (programming language)_item_2_24
  • In Python, == compares by value, versus Java, which compares numerics by value and objects by reference. (Value comparisons in Java on objects can be performed with the equals() method.) Python's is operator may be used to compare object identities (comparison by reference). In Python, comparisons may be chained, for example a <= b <= c.Python (programming language)_item_2_25
  • Python uses the words and, or, not for its boolean operators rather than the symbolic &&, ||, ! used in Java and C.Python (programming language)_item_2_26
  • Python has a type of expression termed a list comprehension. Python 2.4 extended list comprehensions into a more general expression termed a generator expression.Python (programming language)_item_2_27
  • Anonymous functions are implemented using lambda expressions; however, these are limited in that the body can only be one expression.Python (programming language)_item_2_28
  • Conditional expressions in Python are written as x if c else y (different in order of operands from the c ? x : y operator common to many other languages).Python (programming language)_item_2_29
  • Python makes a distinction between lists and tuples. Lists are written as [1, 2, 3], are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples are written as (1, 2, 3), are immutable and thus can be used as the keys of dictionaries, provided all elements of the tuple are immutable. The + operator can be used to concatenate two tuples, which does not directly modify their contents, but rather produces a new tuple containing the elements of both provided tuples. Thus, given the variable t initially equal to (1, 2, 3), executing t = t + (4, 5) first evaluates t + (4, 5), which yields (1, 2, 3, 4, 5), which is then assigned back to t, thereby effectively "modifying the contents" of t, while conforming to the immutable nature of tuple objects. Parentheses are optional for tuples in unambiguous contexts.Python (programming language)_item_2_30
  • Python features sequence unpacking wherein multiple expressions, each evaluating to anything that can be assigned to (a variable, a writable property, etc.), are associated in an identical manner to that forming tuple literals and, as a whole, are put on the left-hand side of the equal sign in an assignment statement. The statement expects an iterable object on the right-hand side of the equal sign that produces the same number of values as the provided writable expressions when iterated through and will iterate through it, assigning each of the produced values to the corresponding expression on the left.Python (programming language)_item_2_31
  • Python has a "string format" operator %. This functions analogously to printf format strings in C, e.g. "spam=%s eggs=%d" % ("blah", 2) evaluates to "spam=blah eggs=2". In Python 3 and 2.6+, this was supplemented by the format() method of the str class, e.g. "spam={0} eggs={1}".format("blah", 2). Python 3.6 added "f-strings": blah = "blah"; eggs = 2; f'spam={blah} eggs={eggs}'.Python (programming language)_item_2_32
  • Strings in Python can be concatenated, by "adding" them (same operator as for adding integers and floats). E.g. ‹code›print('spam'+'eggs') gives ‹code›spameggs. Even if your strings contain numbers, they are still added as strings rather than integers. ‹code›print("2"+"2") gives ‹code›22‹/code›.Python (programming language)_item_2_33
  • Python has various kinds of string literals:Python (programming language)_item_2_34
    • Strings delimited by single or double quote marks. Unlike in Unix shells, Perl and Perl-influenced languages, single quote marks and double quote marks function identically. Both kinds of string use the backslash (\) as an escape character. String interpolation became available in Python 3.6 as "formatted string literals".Python (programming language)_item_2_35
    • Triple-quoted strings, which begin and end with a series of three single or double quote marks. They may span multiple lines and function like here documents in shells, Perl and Ruby.Python (programming language)_item_2_36
    • Raw string varieties, denoted by prefixing the string literal with an r. Escape sequences are not interpreted; hence raw strings are useful where literal backslashes are common, such as regular expressions and Windows-style paths. Compare "@-quoting" in C#.Python (programming language)_item_2_37
  • Python has array index and array slicing expressions on lists, denoted as a[key], a[start:stop] or a[start:stop:step]. Indexes are zero-based, and negative indexes are relative to the end. Slices take elements from the start index up to, but not including, the stop index. The third slice parameter, called step or stride, allows elements to be skipped and reversed. Slice indexes may be omitted, for example a[:] returns a copy of the entire list. Each element of a slice is a shallow copy.Python (programming language)_item_2_38

In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp, Scheme, or Ruby. Python (programming language)_sentence_69

This leads to duplicating some functionality. Python (programming language)_sentence_70

For example: Python (programming language)_sentence_71

Python (programming language)_unordered_list_3

  • List comprehensions vs. for-loopsPython (programming language)_item_3_39
  • Conditional expressions vs. if blocksPython (programming language)_item_3_40
  • The eval() vs. exec() built-in functions (in Python 2, exec is a statement); the former is for expressions, the latter is for statements.Python (programming language)_item_3_41

Statements cannot be a part of an expression, so list and other comprehensions or lambda expressions, all being expressions, cannot contain statements. Python (programming language)_sentence_72

A particular case of this is that an assignment statement such as a = 1 cannot form part of the conditional expression of a conditional statement. Python (programming language)_sentence_73

This has the advantage of avoiding a classic C error of mistaking an assignment operator = for an equality operator == in conditions: if (c = 1) { ... } is syntactically valid (but probably unintended) C code but if c = 1: ... causes a syntax error in Python. Python (programming language)_sentence_74

Methods Python (programming language)_section_6

Methods on objects are functions attached to the object's class; the syntax instance.method(argument) is, for normal methods and functions, syntactic sugar for Class.method(instance, argument). Python (programming language)_sentence_75

Python methods have an explicit self parameter to access instance data, in contrast to the implicit self (or this) in some other object-oriented programming languages (e.g., C++, Java, Objective-C, or Ruby). Python (programming language)_sentence_76

Typing Python (programming language)_section_7

Python uses duck typing and has typed objects but untyped variable names. Python (programming language)_sentence_77

Type constraints are not checked at compile time; rather, operations on an object may fail, signifying that the given object is not of a suitable type. Python (programming language)_sentence_78

Despite being dynamically typed, Python is strongly typed, forbidding operations that are not well-defined (for example, adding a number to a string) rather than silently attempting to make sense of them. Python (programming language)_sentence_79

Python allows programmers to define their own types using classes, which are most often used for object-oriented programming. Python (programming language)_sentence_80

New instances of classes are constructed by calling the class (for example, SpamClass() or EggsClass()), and the classes are instances of the metaclass type (itself an instance of itself), allowing metaprogramming and reflection. Python (programming language)_sentence_81

Before version 3.0, Python had two kinds of classes: old-style and new-style. Python (programming language)_sentence_82

The syntax of both styles is the same, the difference being whether the class object is inherited from, directly or indirectly (all new-style classes inherit from object and are instances of type). Python (programming language)_sentence_83

In versions of Python 2 from Python 2.2 onwards, both kinds of classes can be used. Python (programming language)_sentence_84

Old-style classes were eliminated in Python 3.0. Python (programming language)_sentence_85

The long-term plan is to support gradual typing and from Python 3.5, the syntax of the language allows specifying static types but they are not checked in the default implementation, CPython. Python (programming language)_sentence_86

An experimental optional static type checker named mypy supports compile-time type checking. Python (programming language)_sentence_87

Python (programming language)_table_general_1

Summary of Python 3's built-in typesPython (programming language)_table_caption_1
TypePython (programming language)_header_cell_1_0_0 MutabilityPython (programming language)_header_cell_1_0_1 DescriptionPython (programming language)_header_cell_1_0_2 Syntax examplesPython (programming language)_header_cell_1_0_3
boolPython (programming language)_cell_1_1_0 immutablePython (programming language)_cell_1_1_1 Boolean valuePython (programming language)_cell_1_1_2 True

FalsePython (programming language)_cell_1_1_3

bytearrayPython (programming language)_cell_1_2_0 mutablePython (programming language)_cell_1_2_1 Sequence of bytesPython (programming language)_cell_1_2_2 bytearray(b'Some ASCII')

bytearray(b"Some ASCII") bytearray([119, 105, 107, 105])Python (programming language)_cell_1_2_3

bytesPython (programming language)_cell_1_3_0 immutablePython (programming language)_cell_1_3_1 Sequence of bytesPython (programming language)_cell_1_3_2 b'Some ASCII'

b"Some ASCII" bytes([119, 105, 107, 105])Python (programming language)_cell_1_3_3

complexPython (programming language)_cell_1_4_0 immutablePython (programming language)_cell_1_4_1 Complex number with real and imaginary partsPython (programming language)_cell_1_4_2 3+2.7jPython (programming language)_cell_1_4_3
dictPython (programming language)_cell_1_5_0 mutablePython (programming language)_cell_1_5_1 Associative array (or dictionary) of key and value pairs; can contain mixed types (keys and values), keys must be a hashable typePython (programming language)_cell_1_5_2 {'key1': 1.0, 3: False}

{}Python (programming language)_cell_1_5_3

ellipsisPython (programming language)_cell_1_6_0 immutablePython (programming language)_cell_1_6_1 An ellipsis placeholder to be used as an index in NumPy arraysPython (programming language)_cell_1_6_2 ...

EllipsisPython (programming language)_cell_1_6_3

floatPython (programming language)_cell_1_7_0 immutablePython (programming language)_cell_1_7_1 Double precision floating point number. The precision is machine dependent but in practice is generally implemented as a 64-bit IEEE 754 number with 53 bits of precisionPython (programming language)_cell_1_7_2 1.414Python (programming language)_cell_1_7_3
frozensetPython (programming language)_cell_1_8_0 immutablePython (programming language)_cell_1_8_1 Unordered set, contains no duplicates; can contain mixed types, if hashablePython (programming language)_cell_1_8_2 frozenset([4.0, 'string', True])Python (programming language)_cell_1_8_3
intPython (programming language)_cell_1_9_0 immutablePython (programming language)_cell_1_9_1 Integer of unlimited magnitudePython (programming language)_cell_1_9_2 42Python (programming language)_cell_1_9_3
listPython (programming language)_cell_1_10_0 mutablePython (programming language)_cell_1_10_1 List, can contain mixed typesPython (programming language)_cell_1_10_2 [4.0, 'string', True]

[]Python (programming language)_cell_1_10_3

NoneTypePython (programming language)_cell_1_11_0 immutablePython (programming language)_cell_1_11_1 An object representing the absence of a value, often called null in other languagesPython (programming language)_cell_1_11_2 NonePython (programming language)_cell_1_11_3
NotImplementedTypePython (programming language)_cell_1_12_0 immutablePython (programming language)_cell_1_12_1 A placeholder that can be returned from overloaded operators to indicate unsupported operand types.Python (programming language)_cell_1_12_2 NotImplementedPython (programming language)_cell_1_12_3
rangePython (programming language)_cell_1_13_0 immutablePython (programming language)_cell_1_13_1 A Sequence of numbers commonly used for looping specific number of times in for loopsPython (programming language)_cell_1_13_2 range(1, 10)

range(10, -5, -2)Python (programming language)_cell_1_13_3

setPython (programming language)_cell_1_14_0 mutablePython (programming language)_cell_1_14_1 Unordered set, contains no duplicates; can contain mixed types, if hashablePython (programming language)_cell_1_14_2 {4.0, 'string', True}

set()Python (programming language)_cell_1_14_3

strPython (programming language)_cell_1_15_0 immutablePython (programming language)_cell_1_15_1 A character string: sequence of Unicode codepointsPython (programming language)_cell_1_15_2 'Wikipedia'

"Wikipedia" """Spanning multiple lines"""Python (programming language)_cell_1_15_3

tuplePython (programming language)_cell_1_16_0 immutablePython (programming language)_cell_1_16_1 Can contain mixed typesPython (programming language)_cell_1_16_2 (4.0, 'string', True)

('single element',) ()Python (programming language)_cell_1_16_3

^a Not directly accessible by name Python (programming language)_sentence_88

Arithmetic operations Python (programming language)_section_8

Python has the usual symbols for arithmetic operators (+, -, *, /), the floor division operator // and the modulo operation % (where the remainder can be negative, e.g. 4 % -3 == -2). Python (programming language)_sentence_89

It also has ** for exponentiation, e.g. 5**3 == 125 and 9**0.5 == 3.0, and a matrix multiply operator @ . Python (programming language)_sentence_90

These operators work like in traditional math; with the same precedence rules, the operators infix ( + and - can also be unary to represent positive and negative numbers respectively). Python (programming language)_sentence_91

The division between integers produces floating-point results. Python (programming language)_sentence_92

The behavior of division has changed significantly over time: Python (programming language)_sentence_93

Python (programming language)_unordered_list_4

  • Python 2.1 and earlier used C's division behavior. The / operator is integer division if both operands are integers, and floating-point division otherwise. Integer division rounds towards 0, e.g. 7/3 == 2 and -7/3 == -2.Python (programming language)_item_4_42
  • Python 2.2 changed integer division to round towards negative infinity, e.g. 7/3 == 2 and -7/3 == -3. The floor division // operator was introduced. So 7//3 == 2, -7//3 == -3, 7.5//3 == 2.0 and -7.5//3 == -3.0. Adding from __future__ import division causes a module to use Python 3.0 rules for division (see next).Python (programming language)_item_4_43
  • Python 3.0 changed / to always be floating-point division, e.g. 5/2 == 2.5.Python (programming language)_item_4_44

In Python terms, / is true division (or simply division), and // is floor division. Python (programming language)_sentence_94

/ before version 3.0 is classic division. Python (programming language)_sentence_95

Rounding towards negative infinity, though different from most languages, adds consistency. Python (programming language)_sentence_96

For instance, it means that the equation (a + b)//b == a//b + 1 is always true. Python (programming language)_sentence_97

It also means that the equation b*(a//b) + a%b == a is valid for both positive and negative values of a. Python (programming language)_sentence_98

However, maintaining the validity of this equation means that while the result of a%b is, as expected, in the half-open interval [0, b), where b is a positive integer, it has to lie in the interval (b, 0] when b is negative. Python (programming language)_sentence_99

Python provides a round function for rounding a float to the nearest integer. Python (programming language)_sentence_100

For tie-breaking, Python 3 uses round to even: round(1.5) and round(2.5) both produce 2. Python (programming language)_sentence_101

Versions before 3 used round-away-from-zero: round(0.5) is 1.0, round(-0.5) is −1.0. Python (programming language)_sentence_102

Python allows boolean expressions with multiple equality relations in a manner that is consistent with general use in mathematics. Python (programming language)_sentence_103

For example, the expression a < b < c tests whether a is less than b and b is less than c. C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c. Python (programming language)_sentence_104

Python uses arbitrary-precision arithmetic for all integer operations. Python (programming language)_sentence_105

The Decimal type/class in the decimal module provides decimal floating point numbers to a pre-defined arbitrary precision and several rounding modes. Python (programming language)_sentence_106

The Fraction class in the fractions module provides arbitrary precision for rational numbers. Python (programming language)_sentence_107

Due to Python's extensive mathematics library, and the third-party library NumPy that further extends the native capabilities, it is frequently used as a scientific scripting language to aid in problems such as numerical data processing and manipulation. Python (programming language)_sentence_108

Programming examples Python (programming language)_section_9

Hello world program: Python (programming language)_sentence_109

Program to calculate the factorial of a positive integer: Python (programming language)_sentence_110

Libraries Python (programming language)_section_10

Python's large standard library, commonly cited as one of its greatest strengths, provides tools suited to many tasks. Python (programming language)_sentence_111

For Internet-facing applications, many standard formats and protocols such as MIME and HTTP are supported. Python (programming language)_sentence_112

It includes modules for creating graphical user interfaces, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals, manipulating regular expressions, and unit testing. Python (programming language)_sentence_113

Some parts of the standard library are covered by specifications (for example, the Web Server Gateway Interface (WSGI) implementation wsgiref follows PEP 333), but most modules are not. Python (programming language)_sentence_114

They are specified by their code, internal documentation, and test suites. Python (programming language)_sentence_115

However, because most of the standard library is cross-platform Python code, only a few modules need altering or rewriting for variant implementations. Python (programming language)_sentence_116

As of November 2019, the Python Package Index (PyPI), the official repository for third-party Python software, contains over 200,000 packages with a wide range of functionality, including: Python (programming language)_sentence_117

Python (programming language)_unordered_list_5

Development environments Python (programming language)_section_11

See also: Comparison of integrated development environments § Python Python (programming language)_sentence_118

Most Python implementations (including CPython) include a read–eval–print loop (REPL), permitting them to function as a command line interpreter for which the user enters statements sequentially and receives results immediately. Python (programming language)_sentence_119

Other shells, including IDLE and IPython, add further abilities such as improved auto-completion, session state retention and syntax highlighting. Python (programming language)_sentence_120

As well as standard desktop integrated development environments, there are Web browser-based IDEs; SageMath (intended for developing science and math-related Python programs); PythonAnywhere, a browser-based IDE and hosting environment; and Canopy IDE, a commercial Python IDE emphasizing scientific computing. Python (programming language)_sentence_121

Implementations Python (programming language)_section_12

See also: List of Python software § Python implementations Python (programming language)_sentence_122

Reference implementation Python (programming language)_section_13

CPython is the reference implementation of Python. Python (programming language)_sentence_123

It is written in C, meeting the C89 standard with several select C99 features. Python (programming language)_sentence_124

It compiles Python programs into an intermediate bytecode which is then executed by its virtual machine. Python (programming language)_sentence_125

CPython is distributed with a large standard library written in a mixture of C and native Python. Python (programming language)_sentence_126

It is available for many platforms, including Windows (since Python 3.9.1 version, Python "actively disallows installation on Windows 7"; and did support Windows XP and older, with by now unsupported Python 2.7) and most modern Unix-like systems, including macOS (and Apple M1 Macs, since Python 3.9.1, with experimental installer) and unofficial support for e.g. VMS. Python (programming language)_sentence_127

Platform portability was one of its earliest priorities, in Python 1 and 2 time-frame, even supporting OS/2 and Solaris; support has since been dropped for a lot of platforms. Python (programming language)_sentence_128

Other implementations Python (programming language)_section_14

PyPy is a fast, compliant interpreter of Python 2.7 and 3.6. Python (programming language)_sentence_129

Its just-in-time compiler brings a significant speed improvement over CPython but several libraries written in C cannot be used with it. Python (programming language)_sentence_130

Stackless Python is a significant fork of CPython that implements microthreads; it does not use the C memory stack, thus allowing massively concurrent programs. Python (programming language)_sentence_131

PyPy also has a stackless version. Python (programming language)_sentence_132

MicroPython and CircuitPython are Python 3 variants optimized for microcontrollers. Python (programming language)_sentence_133

This includes Lego Mindstorms EV3. Python (programming language)_sentence_134

Unsupported implementations Python (programming language)_section_15

Other just-in-time Python compilers have been developed, but are now unsupported: Python (programming language)_sentence_135

Python (programming language)_unordered_list_6

  • Google began a project named Unladen Swallow in 2009, with the aim of speeding up the Python interpreter fivefold by using the LLVM, and of improving its multithreading ability to scale to thousands of cores, while ordinary implementations suffer from the global interpreter lock.Python (programming language)_item_6_61
  • Psyco was a just-in-time specializing compiler that integrates with CPython and transforms bytecode to machine code at runtime. The emitted code is specialized for certain data types and is faster than the standard Python code.Python (programming language)_item_6_62

In 2005, Nokia released a Python interpreter for the Series 60 mobile phones named PyS60. Python (programming language)_sentence_136

It includes many of the modules from the CPython implementations and some additional modules to integrate with the Symbian operating system. Python (programming language)_sentence_137

The project has been kept up-to-date to run on all variants of the S60 platform, and several third-party modules are available. Python (programming language)_sentence_138

The Nokia N900 also supports Python with GTK widget libraries, enabling programs to be written and run on the target device. Python (programming language)_sentence_139

Cross-compilers to other languages Python (programming language)_section_16

There are several compilers to high-level object languages, with either unrestricted Python, a restricted subset of Python, or a language similar to Python as the source language: Python (programming language)_sentence_140

Python (programming language)_unordered_list_7

  • Cython compiles Python to C and C++.Python (programming language)_item_7_63
  • Google's Grumpy (latest release in 2017) compiles Python 2 to Go.Python (programming language)_item_7_64
  • IronPython follows a similar approach in order to run Python programs on the .NET Common Language Runtime.Python (programming language)_item_7_65
  • Jython enables the use of the Java class library from a Python program.Python (programming language)_item_7_66
  • MyHDL compiles Python to VHDL.Python (programming language)_item_7_67
  • Nuitka compiles Python into C++.Python (programming language)_item_7_68
  • Numba uses LLVM to compile Python to machine code.Python (programming language)_item_7_69
  • Pyjs (latest release in 2012) compiles Python to JavaScript.Python (programming language)_item_7_70
  • Pyrex (latest release in 2010) and Shed Skin (latest release in 2013) compile to C and C++ respectively.Python (programming language)_item_7_71
  • Pythran compiles Python to C++.Python (programming language)_item_7_72
  • RPython can be compiled to C, and is used to build the PyPy interpreter of Python.Python (programming language)_item_7_73

Performance Python (programming language)_section_17

A performance comparison of various Python implementations on a non-numerical (combinatorial) workload was presented at EuroSciPy '13. Python (programming language)_sentence_141

Python's performance compared to other programming languages has also been benchmarked by The Computer Language Benchmarks Game. Python (programming language)_sentence_142

Development Python (programming language)_section_18

Python's development is conducted largely through the Python Enhancement Proposal (PEP) process, the primary mechanism for proposing major new features, collecting community input on issues and documenting Python design decisions. Python (programming language)_sentence_143

Python coding style is covered in PEP 8. Python (programming language)_sentence_144

Outstanding PEPs are reviewed and commented on by the Python community and the steering council. Python (programming language)_sentence_145

Enhancement of the language corresponds with development of the CPython reference implementation. Python (programming language)_sentence_146

The mailing list python-dev is the primary forum for the language's development. Python (programming language)_sentence_147

Specific issues are discussed in the Roundup bug tracker hosted at . Python (programming language)_sentence_148

Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to GitHub in January 2017. Python (programming language)_sentence_149

CPython's public releases come in three types, distinguished by which part of the version number is incremented: Python (programming language)_sentence_150

Python (programming language)_unordered_list_8

  • Backward-incompatible versions, where code is expected to break and need to be manually ported. The first part of the version number is incremented. These releases happen infrequently—for example, version 3.0 was released 8 years after 2.0.Python (programming language)_item_8_74
  • Major or "feature" releases, about every 18 months, are largely compatible but introduce new features. The second part of the version number is incremented. Each major version is supported by bugfixes for several years after its release.Python (programming language)_item_8_75
  • Bugfix releases, which introduce no new features, occur about every 3 months and are made when a sufficient number of bugs have been fixed upstream since the last release. Security vulnerabilities are also patched in these releases. The third and final part of the version number is incremented.Python (programming language)_item_8_76

Python 3.9 alpha1 was announced in November 2019 and with the adoption of a new yearly release cadence, the first release of 3.9 is slated for November 2020. Python (programming language)_sentence_151

Many alpha, beta, and release-candidates are also released as previews and for testing before final releases. Python (programming language)_sentence_152

Although there is a rough schedule for each release, they are often delayed if the code is not ready. Python (programming language)_sentence_153

Python's development team monitors the state of the code by running the large unit test suite during development, and using the BuildBot continuous integration system. Python (programming language)_sentence_154

The major academic conference on Python is PyCon. Python (programming language)_sentence_155

There are also special Python mentoring programmes, such as Pyladies. Python (programming language)_sentence_156

API documentation generators Python (programming language)_section_19

Python API documentation generators include: Python (programming language)_sentence_157

Python (programming language)_unordered_list_9

  • pydocPython (programming language)_item_9_77
  • SphinxPython (programming language)_item_9_78

Naming Python (programming language)_section_20

Python's name is derived from the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. Python (programming language)_sentence_158

Monty Python references appear frequently in Python code and culture; for example, the metasyntactic variables often used in Python literature are spam and eggs instead of the traditional foo and bar. Python (programming language)_sentence_159

The official Python documentation also contains various references to Monty Python routines. Python (programming language)_sentence_160

The prefix Py- is used to show that something is related to Python. Python (programming language)_sentence_161

Examples of the use of this prefix in names of Python applications or libraries include Pygame, a binding of SDL to Python (commonly used to create games); PyQt and PyGTK, which bind Qt and GTK to Python respectively; and PyPy, a Python implementation originally written in Python. Python (programming language)_sentence_162

Uses Python (programming language)_section_21

Main article: List of Python software Python (programming language)_sentence_163

Since 2003, Python has consistently ranked in the top ten most popular programming languages in the TIOBE Programming Community Index where, as of February 2020, it is the third most popular language (behind Java, and C). Python (programming language)_sentence_164

It was selected Programming Language of the Year in 2007, 2010, and 2018. Python (programming language)_sentence_165

An empirical study found that scripting languages, such as Python, are more productive than conventional languages, such as C and Java, for programming problems involving string manipulation and search in a dictionary, and determined that memory consumption was often "better than Java and not much worse than C or C++". Python (programming language)_sentence_166

Large organizations that use Python include Wikipedia, Google, Yahoo! Python (programming language)_sentence_167 , CERN, NASA, Facebook, Amazon, Instagram, Spotify and some smaller entities like ILM and ITA. Python (programming language)_sentence_168

The social news networking site Reddit is written entirely in Python. Python (programming language)_sentence_169

Python can serve as a scripting language for web applications, e.g., via mod_wsgi for the Apache web server. Python (programming language)_sentence_170

With Web Server Gateway Interface, a standard API has evolved to facilitate these applications. Python (programming language)_sentence_171

Web frameworks like Django, Pylons, Pyramid, TurboGears, web2py, Tornado, Flask, Bottle and Zope support developers in the design and maintenance of complex applications. Python (programming language)_sentence_172

Pyjs and IronPython can be used to develop the client-side of Ajax-based applications. Python (programming language)_sentence_173

SQLAlchemy can be used as a data mapper to a relational database. Python (programming language)_sentence_174

Twisted is a framework to program communications between computers, and is used (for example) by Dropbox. Python (programming language)_sentence_175

Libraries such as NumPy, SciPy and Matplotlib allow the effective use of Python in scientific computing, with specialized libraries such as Biopython and Astropy providing domain-specific functionality. Python (programming language)_sentence_176

SageMath is a mathematical software with a notebook interface programmable in Python: its library covers many aspects of mathematics, including algebra, combinatorics, numerical mathematics, number theory, and calculus. Python (programming language)_sentence_177

OpenCV has python bindings with a rich set of features for computer vision and image processing. Python (programming language)_sentence_178

Python has been successfully embedded in many software products as a scripting language, including in finite element method software such as Abaqus, 3D parametric modeler like FreeCAD, 3D animation packages such as 3ds Max, Blender, Cinema 4D, Lightwave, Houdini, Maya, modo, MotionBuilder, Softimage, the visual effects compositor Nuke, 2D imaging programs like GIMP, Inkscape, Scribus and Paint Shop Pro, and musical notation programs like scorewriter and capella. Python (programming language)_sentence_179

GNU Debugger uses Python as a pretty printer to show complex structures such as C++ containers. Python (programming language)_sentence_180

Esri promotes Python as the best choice for writing scripts in ArcGIS. Python (programming language)_sentence_181

It has also been used in several video games, and has been adopted as first of the three available programming languages in Google App Engine, the other two being Java and Go. Python (programming language)_sentence_182

Python is commonly used in artificial intelligence projects and machine learning projects with the help of libraries like TensorFlow, Keras, Pytorch and Scikit-learn. Python (programming language)_sentence_183

As a scripting language with modular architecture, simple syntax and rich text processing tools, Python is often used for natural language processing. Python (programming language)_sentence_184

Many operating systems include Python as a standard component. Python (programming language)_sentence_185

It ships with most Linux distributions, AmigaOS 4 (using Python 2.7), FreeBSD (as a package), NetBSD, OpenBSD (as a package) and macOS and can be used from the command line (terminal). Python (programming language)_sentence_186

Many Linux distributions use installers written in Python: Ubuntu uses the Ubiquity installer, while Red Hat Linux and Fedora use the Anaconda installer. Python (programming language)_sentence_187

Gentoo Linux uses Python in its package management system, Portage. Python (programming language)_sentence_188

Python is used extensively in the information security industry, including in exploit development. Python (programming language)_sentence_189

Most of the Sugar software for the One Laptop per Child XO, now developed at Sugar Labs, is written in Python. Python (programming language)_sentence_190

The Raspberry Pi single-board computer project has adopted Python as its main user-programming language. Python (programming language)_sentence_191

LibreOffice includes Python, and intends to replace Java with Python. Python (programming language)_sentence_192

Its Python Scripting Provider is a core feature since Version 4.0 from 7 February 2013. Python (programming language)_sentence_193

Languages influenced by Python Python (programming language)_section_22

Python's design and philosophy have influenced many other programming languages: Python (programming language)_sentence_194

Python (programming language)_unordered_list_10

  • Boo uses indentation, a similar syntax, and a similar object model.Python (programming language)_item_10_79
  • Cobra uses indentation and a similar syntax, and its Acknowledgements document lists Python first among languages that influenced it.Python (programming language)_item_10_80
  • CoffeeScript, a programming language that cross-compiles to JavaScript, has Python-inspired syntax.Python (programming language)_item_10_81
  • ECMAScript/JavaScript borrowed iterators and generators from Python.Python (programming language)_item_10_82
  • GDScript, a scripting language very similar to Python, built-in to the Godot game engine.Python (programming language)_item_10_83
  • Go is designed for the "speed of working in a dynamic language like Python" and shares the same syntax for slicing arrays.Python (programming language)_item_10_84
  • Groovy was motivated by the desire to bring the Python design philosophy to Java.Python (programming language)_item_10_85
  • Julia was designed to be "as usable for general programming as Python".Python (programming language)_item_10_86
  • Nim uses indentation and similar syntax.Python (programming language)_item_10_87
  • Ruby's creator, Yukihiro Matsumoto, has said: "I wanted a scripting language that was more powerful than Perl, and more object-oriented than Python. That's why I decided to design my own language."Python (programming language)_item_10_88
  • Swift, a programming language developed by Apple, has some Python-inspired syntax.Python (programming language)_item_10_89

Python's development practices have also been emulated by other languages. Python (programming language)_sentence_195

For example, the practice of requiring a document describing the rationale for, and issues surrounding, a change to the language (in Python, a PEP) is also used in Tcl, Erlang, and Swift. Python (programming language)_sentence_196

See also Python (programming language)_section_23

Python (programming language)_unordered_list_11

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: (programming language).