Python

Python (programming language
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Python

Paradigm	Multi-paradigm:?object-oriented,[1]?procedural?(imperative),?functional,?structured,?reflective
Designed?by	Guido van Rossum
Developer	Python Software Foundation
First?appeared	20?February 1991; 31 years ago[2]

Stable release	
3.10.4[3]??/ 24 March 2022; 20 days ago

Preview release	
3.11.0a4[4]??/ 14 January 2022; 2 months ago

Typing discipline	Duck,?dynamic,?strong typing;[5]?gradual?(since 3.5, but ignored in?CPython)[6]
OS	Windows,?Linux/UNIX,?macOS?and more[7]
License	Python Software Foundation License
Filename extensions	.py, .pyi, .pyc, .pyd, .pyo (prior to 3.5),[8]?.pyw, .pyz (since 3.5)[9]
Website	www.python.org
Major?implementations
CPython,?PyPy,?Stackless Python,?MicroPython,?CircuitPython,?IronPython,?Jython
Dialects
Cython,?RPython,?Starlark[10]
Influenced by
ABC,[11]?Ada,[12]?ALGOL 68,[13]?APL,[14]?C,[15]?C++,[16]?CLU,[17]?Dylan,[18]?Haskell,[19]?Icon,[20]?Lisp,[21]?Modula-3,[16]?Perl,?Standard ML[14]
Influenced
Apache Groovy,?Boo,?Cobra,?CoffeeScript,[22]?D,?F#,?Genie,[23]?Go,?JavaScript,[24][25]?Julia,[26]?Nim,?Ring,[27]?Ruby,[28]?Swift[29]

?Python Programming?at Wikibooks

Python?is a?high-level,?general-purpose programming language. Its design philosophy emphasizes?code readability?with the use of?significant indentation. Its?language constructs?and?object-oriented?approach aim to help?programmers?write clear, logical code for small- and large-scale projects.[30]

Python is?dynamically-typed?and?garbage-collected. It supports multiple?programming paradigms, including?structured?(particularly?procedural), object-oriented and?functional programming. It is often described as a "batteries included" language due to its comprehensive?standard library.[31][32]

Guido van Rossum?began working on Python in the late 1980s as a successor to the?ABC programming language?and first released it in 1991 as Python?0.9.0.[33]?Python?2.0 was released in 2000 and introduced new features such as?list comprehensions,?cycle-detecting?garbage collection,?reference counting, and?Unicode?support. Python?3.0, released in 2008, was a major revision that is not completely?backward-compatible?with earlier versions. Python?2 was discontinued with version?2.7.18 in 2020.[34]

Python consistently ranks as one of the most popular programming languages.[35][36][37][38]

Contents
1	History
2	Design philosophy and features
3	Syntax and semantics
3.1	Indentation
3.2	Statements and control flow
3.3	Expressions
3.4	Methods
3.5	Typing
3.6	Arithmetic operations
4	Programming examples
5	Libraries
6	Development environments
7	Implementations
7.1	Reference implementation
7.2	Other implementations
7.3	Unsupported implementations
7.4	Cross-compilers to other languages
7.5	Performance
8	Development
9	API documentation generators
10	Naming
11	Popularity
12	Uses
13	Languages influenced by Python
14	See also
15	References
15.1	Sources
16	Further reading
17	External links
History[edit]
The designer of Python,?Guido van Rossum, at?OSCON?2006
Main article:?History of Python

Python was conceived in the late 1980s[39]?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,[40]?capable of?exception handling?and interfacing with the?Amoeba?operating system.[11]?Its implementation began in December?1989.[41]?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.[42]?In January?2019, active Python core developers elected a five-member Steering Council to lead the project.[43][44]

Python?2.0 was released on 16 October 2000, with many major new features.[45]?Python?3.0, released on 3 December 2008, with many of its major features?backported?to Python?2.6.x[46]?and 2.7.x. Releases of Python?3 include the?2to3?utility, which automates the translation of Python?2 code to Python?3.[47]

Python?2.7's?end-of-life?was initially set for 2015, then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python?3.[48][49]?No further security patches or other improvements will be released for it.[50][51]?With Python?2's?end-of-life, only Python?3.6.x[52]?and later are supported.

Python?3.9.2 and 3.8.8 were expedited[53]?as all versions of Python (including 2.7[54]) had security issues leading to possible?remote code execution[55]?and?web cache poisoning.[56]

Design philosophy and features[edit]

Python is a?multi-paradigm programming language.?Object-oriented programming?and?structured programming?are fully supported, and many of its features support functional programming and?aspect-oriented programming?(including by?metaprogramming[57]?and?metaobjects?[magic methods] ).[58]?Many other paradigms are supported via extensions, including?design by contract[59][60]?and?logic programming.[61]

Python uses?dynamic typing, and a combination of?reference counting?and a cycle-detecting garbage collector for?memory management.[62]?It uses dynamic?name resolution?(late binding), which binds method and variable names during program execution.

Its design offers some support for functional programming in the?Lisp?tradition. It has?filter,mapandreduce?functions;?list comprehensions,?dictionaries, sets, and?generator?expressions.[63]?The standard library has two modules (itertools?and?functools) that implement functional tools borrowed from?Haskell?and?Standard ML.[64]

Its core philosophy is summarized in the document?The?Zen of Python?(PEP 20), which includes?aphorisms?such as:[65]

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Readability counts.

Rather than building all of its functionality into its core, Python was designed to be highly?extensible?via modules. This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. 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.[39]

Python strives for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. 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" philosophy.[65]?Alex Martelli, a?Fellow?at the?Python Software Foundation?and Python book author, wrote: "To describe something as 'clever' is?not?considered a compliment in the Python culture."[66]

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.[67]?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.?Cython?is also available, which translates a Python script into C and makes direct C-level API calls into the Python interpreter.

Python's developers aim for it to be fun to use. This is reflected in its name—a tribute to the British comedy group?Monty Python[68]—and in occasionally playful approaches to tutorials and reference materials, such as examples that refer to spam and eggs (a reference to a?Monty Python sketch) instead of the standard?foo and bar.[69][70]

A common?neologism?in the Python community is?pythonic, which has a wide range of meanings related to program style. "Pythonic" code may use Python idioms well, be natural or show fluency in the language, or conform with Python's minimalist philosophy and emphasis on readability. Code that is difficult to understand or reads like a rough transcription from another programming language is called?unpythonic.[71][72]

Python users and admirers, especially those considered knowledgeable or experienced, are often referred to as?Pythonistas.[73][74]

Syntax and semantics[edit]
Main article:?Python syntax and semantics

Python is meant to be an easily readable language. Its formatting is visually uncluttered, and often uses English keywords where other languages use punctuation. Unlike many other languages, it does not use?curly brackets?to delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases than?C?or?Pascal.[75]

Indentation[edit]
Main article:?Python syntax and semantics §?Indentation

Python uses?whitespace?indentation, rather than?curly brackets?or keywords, to delimit?blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block.[76]?Thus, the program's visual structure accurately represents its semantic structure.[77]?This feature is sometimes termed the?off-side rule. Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces.[78]

Statements and control flow[edit]

Python's?statements?include:

The?assignment?statement, using a single equals sign?=
The?if?statement, which conditionally executes a block of code, along with?else?and?elif?(a contraction of else-if)
The?for?statement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block
The?while?statement, which executes a block of code as long as its condition is true
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 is always run regardless of how the block exits
The?raise?statement, used to raise a specified exception or re-raise a caught exception
The?class?statement, which executes a block of code and attaches its local namespace to a?class, for use in object-oriented programming
The?def?statement, which defines a?function?or?method
The?with?statement, which encloses a code block within a context manager (for example, acquiring a?lock?before it is run, then releasing the lock; or opening and closing a?file), allowing?resource-acquisition-is-initialization?(RAII)-like behavior and replacing a common try/finally idiom[79]
The?break?statement, which exits a loop
The?continue?statement, which skips the current iteration and continues with the next
The?del?statement, which removes a variable—deleting the reference from the name to the value, and producing an error if the variable is referred to before it is redefined
The?pass?statement, serving as a?NOP, syntactically needed to create an empty code block
The?assert?statement, used in debugging to check for conditions that should apply
The?yield?statement, which returns a value from a?generator?function (and also an operator); used to implement?coroutines
The?return?statement, used to return a value from a function
The?import?statement, used to import modules whose functions or variables can be used in the current program

The assignment statement (=) binds a name as a?reference?to a separate, dynamically-allocated?object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed?data type; however, it always refers to?some?object with a type. This is called?dynamic typing—in contrast to?statically-typed?languages, where each variable may contain only a value of a certain type.

Python does not support?tail call?optimization or?first-class continuations, and, according to van Rossum, it never will.[80][81]?However, better support for?coroutine-like functionality is provided by extending Python's?generators.[82]?Before 2.5, generators were?lazy?iterators; data was passed unidirectionally out of the generator. From Python?2.5 on, it is possible to pass data back into a generator function; and from version 3.3, it can be passed through multiple stack levels.[8)