Python (programming language)

Python

Paradigm	Multi-paradigm:object-oriented,procedural(imperative),functional,structured,reflective
Designed by	Guido van Rossum
Developer	Python Software Foundation
First appeared	20 February 1991(1991-02-20)
Stable release	3.12.4 / 6 June 2024(6 June 2024)
Typing discipline	duck,dynamic,strong;optional type annotations(since 3.5, but those hints are ignored, except with unofficial tools)
OS	Tier 1:64-bitLinux,macOS;64- and 32-bitWindows10+ Tier 2:E.g. 32-bitWebAssembly(WASI)Tier 3:64-bitFreeBSD,iOS;e.g.Raspberry Pi OS Unofficial (or has been known to work): OtherUnix-like/BSDvariants and e.g.Android5.0+ (official from Python 3.13 planned) and a few other platforms
License	Python Software Foundation License
Filename extensions	.py,.pyw,.pyz, .pyi,.pyc,.pyd
Website	python.org
Majorimplementations
CPython,PyPy,Stackless Python,MicroPython,CircuitPython,IronPython,Jython
Dialects
Cython,RPython,Starlark
Influenced by
ABC,Ada,ALGOL 68, APL,C,C++,CLU,Dylan, Haskell,Icon,Lisp, Modula-3,Perl,Standard ML
Influenced
Apache Groovy,Boo,Cobra,CoffeeScript,D,F#,GDScript,Genie,Go,JavaScript,Julia,Mojo,Nim,Ring,Ruby,Swift
Python Programmingat Wikibooks

Pythonis ahigh-level,general-purpose programming language.Its design philosophy emphasizescode readabilitywith the use ofsignificant indentation.

Python isdynamically typedandgarbage-collected.It supports multipleprogramming paradigms,includingstructured(particularlyprocedural),object-orientedandfunctional programming.It is often described as a "batteries included" language due to its comprehensivestandard library.

Guido van Rossumbegan working on Python in the late 1980s as a successor to theABC programming languageand first released it in 1991 as Python 0.9.0.Python 2.0 was released in 2000. Python 3.0, released in 2008, was a major revision not completelybackward-compatiblewith earlier versions. Python 2.7.18, released in 2020, was the last release of Python 2.

Python consistently ranks as one of the most popular programming languages, and has gained widespread use in themachine learningcommunity.

History

The designer of Python,Guido van Rossum,atOSCON2006

Main article:History of Python

Python was invented in the late 1980sbyGuido van RossumatCentrum Wiskunde & Informatica(CWI) in theNetherlandsas a successor to theABC programming language,which was inspired bySETL,capable ofexception handlingand interfacing with theAmoebaoperating system.Its implementation began in December 1989.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"(BDFL), a title the Python community bestowed upon him to reflect his long-term commitment as the project's chief decision-maker(he's since come out of retirement and is self-titled "BDFL-emeritus" ). In January 2019, active Python core developers elected a five-member Steering Council to lead the project.

Python 2.0 was released on 16 October 2000, with many major new features such aslist comprehensions,cycle-detectinggarbage collection,reference counting,andUnicodesupport.Python 3.0, released on 3 December 2008, with many of its major featuresbackportedto Python 2.6.xand 2.7.x. Releases of Python 3 include the2to3utility, which automates the translation of Python 2 code to Python 3.

Python 2.7'send-of-lifewas 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.No further security patches or other improvements will be released for it.Currently only 3.8 and later are supported (2023 security issues were fixed in e.g. 3.7.17, the final 3.7.x release). While Python 2.7 and older is officially unsupported, a different unofficial Python implementation,PyPy,continues to support Python 2, i.e. "2.7.18+" (plus 3.9 and 3.10), with the plus meaning (at least some) "backportedsecurity updates ".

In 2021 (and again twice in 2022), security updates were expedited, since all Python versions were insecure (including 2.7) because of security issues leading to possibleremote code executionandweb-cache poisoning.In 2022, Python 3.10.4 and 3.9.12 were expeditedand 3.8.13, because of many security issues.When Python 3.9.13 was released in May 2022, it was announced that the 3.9 series (joining the older series 3.8 and 3.7) would only receive security fixes in the future.On 7 September 2022, four new releases were made due to a potentialdenial-of-service attack:3.10.7, 3.9.14, 3.8.14, and 3.7.14.

As of October 2023,Python 3.12 is the stable release, and 3.12 and 3.11 are the only versions with active (as opposed to just security) support. Notable changes in 3.11 from 3.10 include increased program execution speed and improved error reporting.

Every Python release since 3.5 has added some syntax to the language. 3.10 added the|union type operatorand thematchandcasekeywords (for structuralpattern matchingstatements). 3.11 expandedexception handlingfunctionality. Python 3.12 added the new keywordtype.

Python 3.11 claims to be between 10 and 60% faster than Python 3.10, and Python 3.12 adds another 5% on top of that. It also has improved error messages, and many other changes.

Since 27 June 2023,Python 3.8 is the oldest supported version of Python (albeit in the 'security support' phase), due to Python 3.7 reachingend-of-life.

Python 3.13 introduced an incremental garbage collector (producing shorter pauses for collection in programs with a lot of objects); an experimentalJIT compiler;and removals from the C API. Some standard library modules and many deprecated classes, functions and methods, will be removed in Python 3.15 and or 3.16.Starting with 3.13, it and later versions have 2 years of full support (up from one and a half); followed by 3 years of security support (for same total support as before).

Design philosophy and features

Python is amulti-paradigm programming language.Object-oriented programmingandstructured programmingare fully supported, and many of their features support functional programming andaspect-oriented programming(includingmetaprogrammingandmetaobjects).Many other paradigms are supported via extensions, includingdesign by contractandlogic programming.

Python usesdynamic typingand a combination ofreference countingand a cycle-detecting garbage collector formemory management.It uses dynamicname resolution(late binding), which binds method and variable names during program execution.

Its design offers some support for functional programming in theLisptradition. It hasfilter,mapandreducefunctions;list comprehensions,dictionaries,sets, andgeneratorexpressions.The standard library has two modules (itertoolsandfunctools) that implement functional tools borrowed fromHaskellandStandard ML.

Its core philosophy is summarized in theZen of Python(PEP 20), which includesaphorismssuch as:

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

However, Python features regularly violate these principles and received criticism for adding unnecessary language bloat.Responses to these criticisms are that the Zen of Python is a guideline rather than a rule.The addition of some new features had been so controversial that Guido van Rossum resigned as Benevolent Dictator for Life following vitriol over the addition of the assignment expression operator in Python 3.8.

Nevertheless, rather than building all of its functionality into its core, Python was designed to be highlyextensiblevia 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 withABC,which espoused the opposite approach.

Python claims to strive for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. In contrast toPerl'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.In practice, however, Python provides many ways to achieve the same task. There are, for example, at least three ways to format a string literal, with no certainty as to which one a programmer should use.Alex Martelli,aFellowat thePython Software Foundationand Python book author, wrote: "To describe something as 'clever' isnotconsidered a compliment in the Python culture. "

Python's developers usually strive to avoidpremature optimizationand reject patches to non-critical parts of theCPythonreference implementation that would offer marginal increases in speed at the cost of clarity.Execution speed can be improved by moving speed-critical functions to extension modules written in languages such as C, or by using ajust-in-time compilerlikePyPy.It is also possible tocross-compile to other languages,but it either doesn't provide the full speed-up that might be expected, since Python is a very dynamic language, or a restricted subset of Python is compiled, and possibly semantics are slightly changed.

Python's developers aim for it to be fun to use. This is reflected in its name—a tribute to the British comedy groupMonty Python—and in occasionally playful approaches to tutorials and reference materials, such as the use of the terms "spam" and "eggs" (a reference toa Monty Python sketch) in examples, instead of the often-used"foo" and "bar".A commonneologismin the Python community ispythonic,which has a wide range of meanings related to program style. "Pythonic" code may use Pythonidiomswell, 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 calledunpythonic.

Syntax and semantics

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 usecurly bracketsto delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases thanCorPascal.

Indentation

Main article:Python syntax and semantics § Indentation

Python useswhitespaceindentation, rather thancurly bracketsor keywords, to delimitblocks.An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block.Thus, the program's visual structure accurately represents its semantic structure.This feature is sometimes termed theoff-side rule.Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces.

Statements and control flow

Python'sstatementsinclude:

• Theassignmentstatement, using a single equals sign=
• Theifstatement, which conditionally executes a block of code, along withelseandelif(a contraction of else-if)
• Theforstatement, which iterates over aniterableobject, capturing each element to a local variable for use by the attached block
• Thewhilestatement, which executes a block of code as long as its condition is true
• Thetrystatement, which allows exceptions raised in its attached code block to be caught and handled byexceptclauses (or new syntaxexcept*in Python 3.11 for exception groups); it also ensures that clean-up code in afinallyblock is always run regardless of how the block exits
• Theraisestatement, used to raise a specified exception or re-raise a caught exception
• Theclassstatement, which executes a block of code and attaches its local namespace to aclass,for use in object-oriented programming
• Thedefstatement, which defines afunctionormethod
• Thewithstatement, which encloses a code block within a context manager (for example, acquiring alockbefore it is run, then releasing the lock; or opening and closing afile), allowingresource-acquisition-is-initialization(RAII)-like behavior and replacing a common try/finally idiom
• Thebreakstatement, which exits a loop
• Thecontinuestatement, which skips the rest of the current iteration and continues with the next
• Thedelstatement, 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
• Thepassstatement, serving as aNOP,syntactically needed to create an empty code block
• Theassertstatement, used in debugging to check for conditions that should apply
• Theyieldstatement, which returns a value from ageneratorfunction (and also an operator); used to implementcoroutines
• Thereturnstatement, used to return a value from a function
• Theimportandfromstatements, used to import modules whose functions or variables can be used in the current program

The assignment statement (=) binds a name as areferenceto a separate, dynamically allocatedobject.Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixeddata type;however, it always refers tosomeobject with a type. This is calleddynamic typing—in contrast tostatically-typedlanguages, where each variable may contain only a value of a certain type.

Python does not supporttail calloptimization orfirst-class continuations,and, according to Van Rossum, it never will.However, better support forcoroutine-like functionality is provided by extending Python'sgenerators.Before 2.5, generators werelazyiterators;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.

Expressions

Python'sexpressionsinclude:

• The+,-,and*operators for mathematical addition, subtraction, and multiplication are similar to other languages, but the behavior of division differs. There are two types of divisions in Python:floor division(or integer division)//and floating-point/division.Python uses the**operator for exponentiation.
• Python uses the+operator for string concatenation. Python uses the*operator for duplicating a string a specified number of times.
• The@infix operator. It is intended to be used by libraries such asNumPyformatrix multiplication.
• The syntax:=,called the "walrus operator", was introduced in Python 3.8. It assigns values to variables as part of a larger expression.
• In Python,==compares by value. Python'sisoperator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example,a<=b<=c.
• Python usesand,or,andnotas Boolean operators.
• Python has a type of expression named alist comprehension,and a more general expression named ageneratorexpression.
• Anonymous functionsare implemented usinglambda expressions;however, there may be only one expression in each body.
• Conditional expressions are written asxifcelsey(different in order of operands from thec? x: yoperator common to many other languages).
• Python makes a distinction betweenlistsandtuples.Lists are written as[1,2,3],are mutable, and cannot be used as the keys of dictionaries (dictionary keys must beimmutablein Python). Tuples, written as(1,2,3),are immutable and thus can be used as keys of dictionaries, provided all of the tuple's elements are immutable. The+operator can be used to concatenate two tuples, which does not directly modify their contents, but produces a new tuple containing the elements of both. Thus, given the variabletinitially equal to(1,2,3),executingt=t+(4,5)first evaluatest+(4,5),which yields(1,2,3,4,5),which is then assigned back tot—thereby effectively "modifying the contents" oftwhile conforming to the immutable nature of tuple objects. Parentheses are optional for tuples in unambiguous contexts.
• Python featuressequence unpackingwhere multiple expressions, each evaluating to anything that can be assigned (to a variable, 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 aniterableobject on the right-hand side of the equal sign that produces the same number of values as the provided writable expressions; when iterated through them, it assigns each of the produced values to the corresponding expression on the left.
• Python has a "string format" operator%that functions analogously toprintfformat strings in C—e.g."spam=%seggs=%d"%("blah",2)evaluates to"spam=blah eggs=2".In Python 2.6+ and 3+, this was supplemented by theformat()method of thestrclass, e.g."spam={0}eggs={1}".format("blah",2).Python 3.6 added "f-strings":spam="blah";eggs=2;f'spam={spam}eggs={eggs}'.
• Strings in Python can beconcatenatedby "adding" them (with the same operator as for adding integers and floats), e.g."spam"+"eggs"returns"spameggs".If strings contain numbers, they are added as strings rather than integers, e.g."2"+"2"returns"22".
• Python has variousstring literals:
  • Delimited by single or double quotes; unlike inUnix shells,Perl,and Perl-influenced languages, single and double quotes work the same. Both use the backslash (\) as anescape character.String interpolationbecame available in Python 3.6 as "formatted string literals".
  • Triple-quoted (beginning and ending with three single or double quotes), which may span multiple lines and function likehere documentsin shells, Perl, andRuby.
  • Raw stringvarieties, denoted by prefixing the string literal withr.Escape sequences are not interpreted; hence raw strings are useful where literal backslashes are common, such asregular expressionsandWindows-style paths. (Compare "@-quoting "inC#.)
• Python hasarray indexandarray slicingexpressions in lists, denoted asa[key],a[start:stop]ora[start:stop:step].Indexes arezero-based,and negative indexes are relative to the end. Slices take elements from thestartindex up to, but not including, thestopindex. The third slice parameter, calledsteporstride,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 ashallow copy.

In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such asCommon Lisp,Scheme,orRuby.This leads to duplicating some functionality. For example:

• List comprehensionsvs.for-loops
• Conditionalexpressions vs.ifblocks
• Theeval()vs.exec()built-in functions (in Python 2,execis a statement); the former is for expressions, the latter is for statements

Statements cannot be a part of an expression—so list and other comprehensions orlambda expressions,all being expressions, cannot contain statements. A particular case is that an assignment statement such asa=1cannot form part of the conditional expression of a conditional statement.

Methods

Methodson objects arefunctionsattached to the object's class; the syntaxinstance.method(argument)is, for normal methods and functions,syntactic sugarforClass.method(instance,argument).Python methods have an explicitselfparameter to accessinstance data,in contrast to the implicit self (orthis) in some other object-oriented programming languages (e.g.,C++,Java,Objective-C,Ruby).Python also provides methods, often calleddunder methods(due to their names beginning and ending with double-underscores), to allow user-defined classes to modify how they are handled by native operations including length, comparison, inarithmetic operationsand type conversion.

Typing

The standard type hierarchy in Python 3

Python usesduck typingand has typed objects but untyped variable names. Type constraints are not checked atcompile time;rather, operations on an object may fail, signifying that it is not of a suitable type. Despite beingdynamically typed,Python isstrongly 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 allows programmers to define their own types usingclasses,most often used forobject-oriented programming.Newinstancesof classes are constructed by calling the class (for example,SpamClass()orEggsClass()), and the classes are instances of themetaclasstype(itself an instance of itself), allowing metaprogramming andreflection.

Before version 3.0, Python had two kinds of classes (both using the same syntax):old-styleandnew-style;current Python versions only support the semantics of the new style.

Python supportsoptional type annotations.These annotations are not enforced by the language, but may be used by external tools such as mypy to catch errors.Mypy also supports a Python compiler called mypyc, which leverages type annotations for optimization.

Summary of Python 3's built-in types

Type	Mutability	Description	Syntax examples
bool	immutable	Boolean value	True False
bytearray	mutable	Sequence ofbytes	bytearray(b'Some ASCII') bytearray(b"Some ASCII") bytearray([119,105,107,105])
bytes	immutable	Sequence of bytes	b'Some ASCII' b"Some ASCII" bytes([119,105,107,105])
complex	immutable	Complex numberwith real and imaginary parts	3+2.7j 3+2.7j
dict	mutable	Associative array(or dictionary) of key and value pairs; can contain mixed types (keys and values), keys must be a hashable type	{'key1':1.0,3:False} {}
types.EllipsisType	immutable	Anellipsisplaceholder to be used as an index inNumPyarrays	... Ellipsis
float	immutable	Double-precisionfloating-point number.The precision is machine-dependent but in practice is generally implemented as a 64-bitIEEE 754number with 53 bits of precision.	1.33333
frozenset	immutable	Unorderedset,contains no duplicates; can contain mixed types, if hashable	frozenset([4.0,'string',True])
int	immutable	Integerof unlimited magnitude	42
list	mutable	List,can contain mixed types	[4.0,'string',True] []
types.NoneType	immutable	An object representing the absence of a value, often callednullin other languages	None
types.NotImplementedType	immutable	A placeholder that can be returned fromoverloaded operatorsto indicate unsupported operand types.	NotImplemented
range	immutable	Animmutable sequenceof numbers commonly used for looping a specific number of times inforloops	range(-1,10) range(10,-5,-2)
set	mutable	Unorderedset,contains no duplicates; can contain mixed types, if hashable	{4.0,'string',True} set()
str	immutable	Acharacter string:sequence of Unicode codepoints	'Wikipedia' "Wikipedia" """Spanning multiple lines "" " Spanning multiple lines
tuple	immutable	Can contain mixed types	(4.0,'string',True) ('single element',) ()

Arithmetic operations

Python has the usual symbols for arithmetic operators (+,-,*,/), the floor division operator//and themodulo operation%(where the remainder can be negative, e.g.4 % -3 == -2). It also has**forexponentiation,e.g.5**3 == 125and9**0.5 == 3.0,and a matrix‑multiplication operator@.These operators work like in traditional math; with the sameprecedence rules,the operatorsinfix(+and-can also beunaryto represent positive and negative numbers respectively).

The division between integers produces floating-point results. The behavior of division has changed significantly over time:

• Current Python (i.e. since 3.0) changed/to always be floating-point division, e.g.5/2==2.5.
• The floor division//operator was introduced. So7//3 == 2,-7//3 == -3,7.5//3 == 2.0and-7.5//3 == -3.0.Addingfrom__future__importdivisioncauses a module used in Python 2.7 to use Python 3.0 rules for division (see above).

In Python terms,/istrue division(or simplydivision), and//isfloor division./before version 3.0 isclassic division.

Rounding towards negative infinity, though different from most languages, adds consistency. For instance, it means that the equation(a+b)//b==a//b+1is always true. It also means that the equationb*(a//b)+a%b==ais valid for both positive and negative values ofa.However, maintaining the validity of this equation means that while the result ofa%bis, as expected, in thehalf-open interval[0,b), wherebis a positive integer, it has to lie in the interval (b,0] whenbis negative.

Python provides aroundfunction forroundinga float to the nearest integer. Fortie-breaking,Python 3 usesround to even:round(1.5)andround(2.5)both produce2.Versions before 3 usedround-away-from-zero:round(0.5)is1.0,round(-0.5)is−1.0.

Python allows Boolean expressions with multiple equality relations in a manner that is consistent with general use in mathematics. For example, the expressiona < b < ctests whetherais less thanbandbis less thanc.C-derived languages interpret this expression differently: in C, the expression would first evaluatea < b,resulting in 0 or 1, and that result would then be compared withc.

Python usesarbitrary-precision arithmeticfor all integer operations. TheDecimaltype/class in thedecimalmodule providesdecimal floating-point numbersto a pre-defined arbitrary precision and several rounding modes.TheFractionclass in thefractionsmodule provides arbitrary precision forrational numbers.

Due to Python's extensive mathematics library, and the third-party libraryNumPythat 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.

Programming examples

"Hello, World!" program:

print('Hello, world!')

Program to calculate thefactorialof a positive integer:

n=int(input('Type a number, and its factorial will be printed: '))

ifn<0:
raiseValueError('You must enter a non-negative integer')

factorial=1
foriinrange(2,n+1):
factorial*=i

print(factorial)

Libraries

Python's large standard libraryprovides tools suited to many tasks and is commonly cited as one of its greatest strengths. For Internet-facing applications, many standard formats and protocols such asMIMEandHTTPare supported. It includes modules for creatinggraphical user interfaces,connecting torelational databases,generating pseudorandom numbers,arithmetic with arbitrary-precision decimals,manipulatingregular expressions,andunit testing.

Some parts of the standard library are covered by specifications—for example, theWeb Server Gateway Interface(WSGI) implementationwsgireffollows PEP 333—but most are specified by their code, internal documentation, andtest suites.However, because most of the standard library is cross-platform Python code, only a few modules need altering or rewriting for variant implementations.

As of 17 March 2024,thePython Package Index(PyPI), the official repository for third-party Python software, contains over 523,000packages with a wide range of functionality, including:

• Automation
• Data analytics
• Databases
• Documentation
• Graphical user interfaces
• Image processing
• Machine learning
• Mobile apps
• Multimedia
• Computer networking
• Scientific computing
• System administration
• Test frameworks
• Text processing
• Web frameworks
• Web scraping

Development environments

See also:Comparison of integrated development environments § Python

Most Python implementations (including CPython) include aread–eval–print loop(REPL), permitting them to function as acommand line interpreterfor which users enter statements sequentially and receive results immediately.

Python also comes with anIntegrated development environment (IDE)calledIDLE,which is more beginner-oriented.

Other shells, includingIDLEandIPython,add further abilities such as improved auto-completion, session state retention, andsyntax highlighting.

As well as standard desktopintegrated development environmentsincluding PyCharm, IntelliJ Idea, Visual Studio Code etc, there areweb browser-based IDEs, includingSageMath,for developing science- and math-related programs;PythonAnywhere,a browser-based IDE and hosting environment; and Canopy IDE, a commercial IDE emphasizingscientific computing.

Implementations

See also:List of Python software § Python implementations

Reference implementation

CPythonis thereference implementationof Python. It is written in C, meeting theC89standard (Python 3.11 usesC11) with several selectC99features. CPython includes its own C extensions, but third-party extensions are not limited to older C versions—e.g. they can be implemented withC11or C++.CPythoncompilesPython programs into an intermediatebytecodewhich is then executed by itsvirtual machine.CPython is distributed with a large standard library written in a mixture of C and native Python, and is available for many platforms, including Windows (starting with Python 3.9, the Python installer deliberately fails to install onWindows 7and 8;Windows XPwas supported until Python 3.5) and most modernUnix-likesystems, including macOS (andApple M1Macs, since Python 3.9.1, with experimental installer), with unofficial support forVMS.Platform portability was one of its earliest priorities.(During Python 1 and 2 development, evenOS/2andSolariswere supported,but support has since been dropped for many platforms.)

Python, since 3.7, only supports operating systems with multi-threading support.

Other implementations

• PyPyis a fast, compliant interpreter of Python 2.7 and 3.8.Itsjust-in-time compileroften brings a significant speed improvement over CPython, but some libraries written in C cannot be used with it.
• Stackless Pythonis a significant fork of CPython that implementsmicrothreads;it does not use thecall stackin the same way, thus allowing massively concurrent programs. PyPy also has a stackless version.
• MicroPythonandCircuitPythonare Python 3 variants optimized formicrocontrollers,includingLego Mindstorms EV3.
• Pyston is a variant of the Python runtime that uses just-in-time compilation to speed up the execution of Python programs.
• Cinder is a performance-oriented fork of CPython 3.8 that contains a number of optimizations, including bytecode inline caching, eager evaluation of coroutines, a method-at-a-timeJIT,and an experimental bytecode compiler.
• SnekEmbedded Computing Language (compatible with e.g. 8-bitAVR microcontrollerssuch asATmega 328P-based Arduino, as well as larger ones compatible withMicroPython) "is Python-inspired, but it is not Python. It is possible to write Snek programs that run under a full Python system, but most Python programs will not run under Snek."It is an imperative language not includingOOP/ classes, unlike Python, and simplifying to one number type with 32-bitsingle-precision(similar toJavaScript,except smaller).

Unsupported implementations

Other just-in-time Python compilers have been developed, but are now unsupported:

• Google began a project namedUnladen Swallowin 2009, with the aim of speeding up the Python interpreter five-fold by using theLLVM,and of improving itsmultithreadingability to scale to thousands of cores,while ordinary implementations suffer from theglobal interpreter lock.
• Psycois a discontinuedjust-in-timespecializingcompiler that integrates with CPython and transforms bytecode to machine code at runtime. The emitted code is specialized for certaindata typesand is faster than the standard Python code. Psyco does not support Python 2.7 or later.
• PyS60was a Python 2 interpreter forSeries 60mobile phones released byNokiain 2005. It implemented many of the modules from the standard library and some additional modules for integrating with theSymbianoperating system. The NokiaN900also supports Python withGTKwidget libraries, enabling programs to be written and run on the target device.

Cross-compilers to other languages

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

• Brython,TranscryptandPyjs(latest release in 2012) compile Python toJavaScript.
• Codoncompiles a subset of statically typed Pythonto machine code (viaLLVM) and supports native multithreading.
• Cythoncompiles (a superset of) Python to C. The resulting code is also usable with Python via direct C-level API calls into the Python interpreter.
• PyJL compiles/transpiles a subset of Python to "human-readable, maintainable, and high-performance Julia source code".Despite claiming high performance, no tool can claim to do that forarbitraryPython code; i.e. it's known not possible to compile to a faster language or machine code. Unless semantics of Python are changed, but in many cases speedup is possible with few or no changes in the Python code. The faster Julia source code can then be used from Python, or compiled to machine code, and based that way.
• Nuitkacompiles Python into C.
• Numbauses LLVM to compile a subset of Python to machine code.
• Pythran compiles a subset of Python 3 to C++ (C++11).
• RPythoncan be compiled to C, and is used to build the PyPy interpreter of Python.
• The Python → 11l → C++ transpilercompiles a subset of Python 3 to C++ (C++17).

Specialized:

• MyHDLis a Python-basedhardware description language(HDL), that converts MyHDL code toVerilogorVHDLcode.

Older projects (or not to be used with Python 3.x and latest syntax):

• Google's Grumpy (latest release in 2017)transpilesPython 2 toGo.
• IronPythonallows running Python 2.7 programs (and analpha,released in 2021, is also available for "Python 3.4, although features and behaviors from later versions may be included") on the.NETCommon Language Runtime.
• Jythoncompiles Python 2.7 to Java bytecode, allowing the use of the Java libraries from a Python program.
• Pyrex(latest release in 2010) andShed Skin(latest release in 2013) compile to C and C++ respectively.

Performance

Performance comparison of various Python implementations on a non-numerical (combinatorial) workload was presented at EuroSciPy '13.Python's performance compared to other programming languages is also benchmarked byThe Computer Language Benchmarks Game.

Development

Python's development is conducted largely through thePython Enhancement Proposal(PEP) process, the primary mechanism for proposing major new features, collecting community input on issues, and documenting Python design decisions.Python coding style is covered in PEP 8.Outstanding PEPs are reviewed and commented on by the Python community and the steering council.

Enhancement of the language corresponds with the development of the CPython reference implementation. The mailing list python-dev is the primary forum for the language's development. Specific issues were originally discussed in theRoundupbug trackerhosted at by the foundation.In 2022, all issues and discussions were migrated toGitHub.Development originally took place on aself-hostedsource-code repository runningMercurial,until Python moved toGitHubin January 2017.

CPython's public releases come in three types, distinguished by which part of the version number is incremented:

• Backward-incompatible versions, where code is expected to break and needs to be manuallyported.The first part of the version number is incremented. These releases happen infrequently—version 3.0 was released 8 years after 2.0. According to Guido van Rossum, a version 4.0 is very unlikely to ever happen.
• Major or "feature" releases are largely compatible with the previous version but introduce new features. The second part of the version number is incremented. Starting with Python 3.9, these releases are expected to happen annually.Each major version is supported by bug fixes for several years after its release.
• 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.

Manyalpha, beta, and release-candidatesare also released as previews and for testing before final releases. Although there is a rough schedule for each release, they are often delayed if the code is not ready. Python's development team monitors the state of the code by running the largeunit testsuite during development.

The majoracademic conferenceon Python isPyCon.There are also special Python mentoring programs, such asPyLadies.

Python 3.12 removedwstrmeaning Python extensionsneed to be modified,and 3.10 addedpattern matchingto the language.

Python 3.12 dropped some outdated modules, and more will be dropped in the future, deprecated as of 3.13; already deprecated array 'u' format code will emitDeprecationWarningsince 3.13 and will be removed in Python 3.16. The 'w' format code should be used instead. Part of ctypes is also deprecated andhttp.server.CGIHTTPRequestHandlerwill emit a DeprecationWarning, and will be removed in 3.15. Using that code already has a high potential for both security and functionality bugs. Parts of the typing module are deprecated, e.g. creating atyping.NamedTupleclass using keyword arguments to denote the fields and such (and more) will be disallowed in Python 3.15.

API documentation generators

Tools that can generate documentation for Python API includepydoc(available as part of the standard library),Sphinx,Pdocand its forks,DoxygenandGraphviz,among others.

Naming

Python's name is derived from the British comedy groupMonty Python,whom Python creator Guido van Rossum enjoyed while developing the language. Monty Python references appear frequently in Python code and culture;for example, themetasyntactic variablesoften used in Python literature arespamandeggsinstead of the traditionalfooandbar.The official Python documentation also contains various references to Monty Python routines.Users of Python are sometimes referred to as "Pythonistas".

The prefixPy-is used to show that something is related to Python. Examples of the use of this prefix in names of Python applications or libraries includePygame,abindingofSDLto Python (commonly used to create games);PyQtandPyGTK,which bindQtand GTK to Python respectively; andPyPy,a Python implementation originally written in Python.

Popularity

Since 2003, Python has consistently ranked in the top ten most popular programming languages in theTIOBE Programming Community Indexwhere as of December 2022it was the most popular language (ahead of C, C++, andJava).It was selected as Programming Language of the Year (for "the highest rise in ratings in a year" ) in 2007, 2010, 2018, and 2020 (the only language to have done so four times as of 2020).

Large organizations that use Python includeWikipedia,Google,Yahoo!,CERN,NASA,Facebook,Amazon,Instagram,Spotify,and some smaller entities likeILMandITA.The social news networking siteRedditwas written mostly in Python.

Uses

Main article:List of Python software

Python Powered

Python can serve as ascripting languageforweb applications,e.g. viamod_wsgifor theApache webserver.WithWeb Server Gateway Interface,a standard API has evolved to facilitate these applications.Web frameworkslikeDjango,Pylons,Pyramid,TurboGears,web2py,Tornado,Flask,Bottle, andZopesupport developers in the design and maintenance of complex applications. Pyjs andIronPythoncan be used to develop the client-side of Ajax-based applications.SQLAlchemycan be used as adata mapperto a relational database.Twistedis a framework to program communications between computers, and is used (for example) byDropbox.

Libraries such asNumPy,SciPyandMatplotliballow the effective use of Python in scientific computing,with specialized libraries such asBiopythonandAstropyproviding domain-specific functionality.SageMathis acomputer algebra systemwith anotebook interfaceprogrammable in Python: its library covers many aspects ofmathematics,includingalgebra,combinatorics,numerical mathematics,number theory,andcalculus.OpenCVhas Python bindings with a rich set of features forcomputer visionandimage processing.

Python is commonly used inartificial intelligenceprojects and machine learning projects with the help of libraries likeTensorFlow,Keras,Pytorch,scikit-learnand the Logic languageProbLog.As a scripting language with amodular architecture,simple syntax, and rich text processing tools, Python is often used fornatural language processing.

The combination of Python andProloghas proved to be particularly useful for AI applications, with Prolog providing knowledge representation and reasoning capablities. The Janus system, in particular, exploits the similarites between these two languages, in part because of their use of dynamic typing, and the simple recursive nature of their data structures. Typical applications of this combination include natural language processing, visual query answering, geospatial reasoning, and handling of semantic web data. The Natlog system, implemented in Python, usesDefinite Clause Grammars(DCGs) as prompt generators for text-to-text generators like GPT3 and text-to-image generators like DALL-E or Stable Diffusion.

Python can also be used forgraphical user interface(GUI) by using libraries likeTkinter.

Python has been successfully embedded in many software products as a scripting language, including infinite element methodsoftware such asAbaqus,3D parametric modelers likeFreeCAD,3D animation packages such as3ds Max,Blender,Cinema 4D,Lightwave,Houdini,Maya,modo,MotionBuilder,Softimage,the visual effects compositorNuke,2D imaging programs likeGIMP,Inkscape,ScribusandPaint Shop Pro,andmusical notationprograms likescorewriterandcapella.GNU Debuggeruses Python as apretty printerto show complex structures such as C++ containers.Esripromotes Python as the best choice for writing scripts inArcGIS.It has also been used in several video games,and has been adopted as first of the three availableprogramming languagesinGoogle App Engine,the other two beingJavaandGo.

Many operating systems include Python as a standard component. It ships with mostLinux distributions,AmigaOS 4(using Python 2.7),FreeBSD(as a package),NetBSD,andOpenBSD(as a package) and can be used from the command line (terminal). Many Linux distributions use installers written in Python:Ubuntuuses theUbiquityinstaller, whileRed Hat LinuxandFedora Linuxuse theAnacondainstaller.Gentoo Linuxuses Python in itspackage management system,Portage.

Python is used extensively in theinformation securityindustry, including in exploit development.

Most of theSugarsoftware for theOne Laptop per ChildXO, developed atSugar Labsas of 2008,is written in Python.TheRaspberry Pisingle-board computerproject has adopted Python as its main user-programming language.

LibreOfficeincludes Python and intends to replace Java with Python. Its Python Scripting Provider is a core featuresince Version 4.0 from 7 February 2013.

Languages influenced by Python

Python's design and philosophy have influenced many other programming languages:

• Boouses indentation, a similar syntax, and a similar object model.
• Cobrauses indentation and a similar syntax, and itsAcknowledgementsdocument lists Python first among languages that influenced it.
• CoffeeScript,a programming language that cross-compiles to JavaScript, has Python-inspired syntax.
• ECMAScript–JavaScriptborrowed iterators andgeneratorsfrom Python.
• GDScript,a scripting language very similar to Python, built-in to theGodotgame engine.
• Gois designed for the "speed of working in a dynamic language like Python"and shares the same syntax for slicing arrays.
• Groovywas motivated by the desire to bring the Python design philosophy toJava.
• Juliawas designed to be "as usable for general programming as Python".
• Mojois a non-strictsuperset of Python (e.g. still missing classes, and adding e.g.struct).
• Nimuses indentation and similar syntax.
• 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."
• Swift,a programming language developed by Apple, has some Python-inspired syntax.
• Kotlinblends Python and Java features, minimizing boilerplate code for enhanced developer efficiency.

Python's development practices have also been emulated by other languages. 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 inTcl,Erlang,and Swift.

See also

• Python syntax and semantics
• pip (package manager)
• List of programming languages
• History of programming languages
• Comparison of programming languages

References

Sources

• "Python for Artificial Intelligence".Python Wiki. 19 July 2012. Archived fromthe originalon 1 November 2012.Retrieved3 December2012.
• Paine, Jocelyn, ed. (August 2005)."AI in Python".AI Expert Newsletter.Amzi!. Archived fromthe originalon 26 March 2012.Retrieved11 February2012.
• "PyAIML 0.8.5: Python Package Index".Pypi.python.org.Retrieved17 July2013.
• Russell, Stuart J.&Norvig, Peter(2009).Artificial Intelligence: A Modern Approach(3rd ed.). Upper Saddle River, NJ: Prentice Hall.ISBN978-0-13-604259-4.

Further reading

• Downey, Allen B. (May 2012).Think Python: How to Think Like a Computer Scientist(version 1.6.6 ed.). Cambridge University Press.ISBN978-0-521-72596-5.
• Hamilton, Naomi (5 August 2008)."The A-Z of Programming Languages: Python".Computerworld.Archived fromthe originalon 29 December 2008.Retrieved31 March2010.
• Lutz, Mark (2013).Learning Python(5th ed.). O'Reilly Media.ISBN978-0-596-15806-4.
• Summerfield, Mark (2009).Programming in Python 3(2nd ed.). Addison-Wesley Professional.ISBN978-0-321-68056-3.
• Ramalho, Luciano (May 2022).Fluent Python.O'Reilly Media.ISBN978-1-4920-5632-4.

External links

• Official website