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Python is a
high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer scien ...
, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. Python is dynamically-typed and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural),
object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
and
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions tha ...
. It is often described as a "batteries included" language due to its comprehensive standard library. 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. Python 2.0 was released in 2000 and introduced new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
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. Python consistently ranks as one of the most popular programming languages.


History

Python was conceived in the late 1980s by Guido van Rossum at
Centrum Wiskunde & Informatica The (abbr. CWI; English: "National Research Institute for Mathematics and Computer Science") is a research centre in the field of mathematics and theoretical computer science. It is part of the institutes organization of the Dutch Research C ...
(CWI) in the
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
as a successor to the ABC programming language, which was inspired by SETL, capable of exception handling (from the start plus new capabilities in Python 3.11) and interfacing with the Amoeba operating 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 Benevolent dictator for life (BDFL) is a title given to a small number of open-source software development leaders, typically project founders who retain the final say in disputes or arguments within the community. The phrase originated in 1995 w ...
", a title the Python community bestowed upon him to reflect his long-term commitment as the project's chief decision-maker. 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. Python 3.0, released on 3 December 2008, with many of its major features backported to Python 2.6.x and 2.7.x. Releases of Python 3 include the 2to3 utility, which automates the translation of Python 2 code to Python 3. 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. No further security patches or other improvements will be released for it. Currently only 3.7 and later are supported. In 2021, Python 3.9.2 and 3.8.8 were expedited as all versions of Python (including 2.7) had security issues leading to possible
remote code execution In computer security, arbitrary code execution (ACE) is an attacker's ability to run any commands or code of the attacker's choice on a target machine or in a target process. An arbitrary code execution vulnerability is a security flaw in soft ...
and web cache poisoning. In 2022, Python 3.10.4 and 3.9.12 were expedited and 3.8.13, and 3.7.13, 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) will only receive security fixes going forward. On September 7, 2022, four new releases were made due to a potential
denial-of-service attack In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host conne ...
: 3.10.7, 3.9.14, 3.8.14, and 3.7.14. Python 3.11.0 is the current stable release and among the notable changes from 3.10 are that it is 10–60% faster and significantly improved error reporting. Python 3.12 (alpha 2) has improved error messages.


Removals from Python

The deprecated smtpd module has been removed from Python 3.12 (alpha). And a number of other old, broken and deprecated functions (e.g. from unittest module), classes and methods have been removed. The deprecated wstr and wstr_ length members of the C implementation of
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
objects were removed, to make
UTF-8 UTF-8 is a variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit''. UTF-8 is capable of e ...
the default in later Python versions. Historically, Python 3 also made changes from Python 2, e.g. changed the division operator.


Design philosophy and features

Python is a multi-paradigm programming language.
Object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
and structured programming are fully supported, and many of their features support functional programming and aspect-oriented programming (including metaprogramming and metaobjects). Many other paradigms are supported via extensions, including design by contract and logic programming. Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management. 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 functions; list comprehensions, dictionaries, sets, and generator expressions. The standard library has two modules ( and ) that implement functional tools borrowed from Haskell and Standard ML. Its core philosophy is summarized in the document ''The Zen of Python'' (''PEP 20''), which includes aphorisms such as: * 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 Extensibility is a software engineering and systems design principle that provides for future growth. Extensibility is a measure of the ability to extend a system and the level of effort required to implement the extension. Extensions can be ...
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. Python strives for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. In contrast to
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
'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. Alex Martelli, a
Fellow A fellow is a concept whose exact meaning depends on context. In learned or professional societies, it refers to a privileged member who is specially elected in recognition of their work and achievements. Within the context of higher education ...
at the Python Software Foundation and Python book author, wrote: "To describe something as 'clever' is ''not'' considered a compliment in the Python culture." 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. 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 In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may c ...
. 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—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. A common
neologism A neologism Ancient_Greek.html"_;"title="_from_Ancient_Greek">Greek_νέο-_''néo''(="new")_and_λόγος_/''lógos''_meaning_"speech,_utterance"is_a_relatively_recent_or_isolated_term,_word,_or_phrase_that_may_be_in_the_process_of_entering_com ...
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''. Python users and admirers, especially those considered knowledgeable or experienced, are often referred to as ''Pythonistas''.


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 Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, Frenc ...
.


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. Thus, the program's visual structure accurately represents its semantic structure. 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.


Statements and control flow

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 (or new syntax except* in Python 3.11 for exception groups); 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 Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...
, 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 * The
break Break or Breaks or The Break may refer to: Time off from duties * Recess (break), time in which a group of people is temporarily dismissed from its duties * Break (work), time off during a shift/recess ** Coffee break, a short mid-morning rest ...
statement, which exits a loop * The continue statement, which skips the rest of 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 Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a '' name'' ...
to a separate, dynamically-allocated
object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...
. 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 In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allowed operations on it. A data type tells the compiler or interpreter how the programmer intends to use the data. Most progra ...
; 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. However, better support for coroutine-like functionality is provided by extending Python's generators. 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.


Expressions

Python's expressions include: * 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 as NumPy for matrix 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's is operator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example, . * Python uses and, or, and not as boolean operators. * Python has a type of expression called a '' list comprehension'', as well as a more general expression called a '' generator expression''. * Anonymous functions are implemented using lambda expressions; however, there may be only one expression in each body. * Conditional expressions are written as (different in order of operands from the c ? x : y operator common to many other languages). * Python makes a distinction between
lists A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations * List College, an undergraduate division of the Jewish Theological Seminary of America * SC Germania List, German rugby union ...
and
tuple In mathematics, a tuple is a finite ordered list (sequence) of elements. An -tuple is a sequence (or ordered list) of elements, where is a non-negative integer. There is only one 0-tuple, referred to as ''the empty tuple''. An -tuple is defi ...
s. Lists are written as , are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples, written as , 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 variable t initially equal to , executing first evaluates , which yields , 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 features ''sequence unpacking'' where 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 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 them, it assigns each of the produced values to the corresponding expression on the left. * Python has a "string format" operator % that functions analogously to printf format strings in C—e.g. evaluates to "spam=blah eggs=2". In Python 2.6+ and 3+, this was supplemented by the format() method of the str class, e.g. . Python 3.6 added "f-strings": . * Strings in Python can be concatenated by "adding" them (with the same operator as for adding integers and floats), e.g. returns "spameggs". If strings contain numbers, they are added as strings rather than integers, e.g. returns "22". * Python has various string literals: ** Delimited by single or double quote marks; unlike in Unix shells,
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
, and Perl-influenced languages, single and double quote marks work the same. Both use the backslash (\) as an escape character. String interpolation became available in Python 3.6 as "formatted string literals". ** Triple-quoted (beginning and ending with three single or double quote marks), which may span multiple lines and function like here documents in shells, Perl, and
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
. ** Raw string varieties, denoted by prefixing the string literal with r. Escape sequences are not interpreted; hence raw strings are useful where literal backslashes are common, such as regular expressions and
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
-style paths. (Compare "@-quoting" in C#.) * Python has array index and array slicing expressions in lists, denoted as a ey/code>, or . 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, returns a copy of the entire list. Each element of a slice is a shallow copy. In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp,
Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...
, or
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
. This leads to duplicating some functionality. For example: * List comprehensions vs. for-loops *
Conditional Conditional (if then) may refer to: *Causal conditional, if X then Y, where X is a cause of Y *Conditional probability, the probability of an event A given that another event B has occurred *Conditional proof, in logic: a proof that asserts a co ...
expressions vs. if blocks * The eval() vs. exec() built-in functions (in Python 2, exec is 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 or lambda expressions, all being expressions, cannot contain statements. A particular case is that an assignment statement such as cannot form part of the conditional expression of a conditional statement. This has the advantage of avoiding a classic C error of mistaking an assignment operator = for an equality operator

in conditions: is syntactically valid (but probably unintended) C code, but causes a syntax error in Python.


Methods

Methods Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more often means a prescribed process for completing a task. It may refer to: *Scien ...
on objects are functions attached to the object's class; the syntax is, for normal methods and functions, syntactic sugar for . 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,
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
). Python also provides methods, often called ''dunder 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, in arithmetic operations and type conversion.


Typing

Python uses duck typing and has typed objects but untyped variable names. Type constraints are not checked at
compile time In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled. The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concep ...
; rather, operations on an object may fail, signifying that it is not of a suitable type. Despite being dynamically typed, Python is
strongly typed In computer programming, one of the many ways that programming languages are colloquially classified is whether the language's type system makes it strongly typed or weakly typed (loosely typed). However, there is no precise technical definition ...
, 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 using classes, most often used for
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
. New instances of classes are constructed by calling the class (for example, or ), and the classes are instances of the metaclass type (itself an instance of itself), allowing metaprogramming and reflection. Before version 3.0, Python had two kinds of classes (both using the same syntax): ''old-style'' and ''new-style'', current Python versions only support the semantics new style. The long-term plan is to support gradual typing. Python's syntax allows specifying static types, but they are not checked in the default implementation, CPython. An experimental optional static type-checker, ''mypy'', supports compile-time type checking.


Arithmetic operations

Python has the usual symbols for arithmetic operators (+, -, *, /), the floor division operator // and the
modulo operation In computing, the modulo operation returns the remainder or signed remainder of a division, after one number is divided by another (called the '' modulus'' of the operation). Given two positive numbers and , modulo (often abbreviated as ) is ...
% (where the remainder can be negative, e.g. 4 % -3

-2
). It also has ** for
exponentiation Exponentiation is a mathematical operation, written as , involving two numbers, the '' base'' and the ''exponent'' or ''power'' , and pronounced as " (raised) to the (power of) ". When is a positive integer, exponentiation corresponds to ...
, e.g. 5**3

125
and 9**0.5

3.0
, and a matrix‑multiplication operator @ . 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). 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. . * 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 causes a module used in Python 2.7 to use Python 3.0 rules for division (see above). In Python terms, / is ''true division'' (or simply ''division''), and // is ''floor division.'' / before version 3.0 is ''classic division''. Rounding towards negative infinity, though different from most languages, adds consistency. For instance, it means that the equation is always true. It also means that the equation is valid for both positive and negative values of a. However, maintaining the validity of this equation means that while the result of a%b is, as expected, in the
half-open interval In mathematics, a (real) interval is a set of real numbers that contains all real numbers lying between any two numbers of the set. For example, the set of numbers satisfying is an interval which contains , , and all numbers in between. Othe ...
, ''b''), where b is a positive integer, it has to lie in the interval (''b'', 0when b is negative. Python provides a round function for rounding a float to the nearest integer. For tie-breaking, Python 3 uses round to even: round(1.5) and round(2.5) both produce 2. Versions before 3 used round-away-from-zero: round(0.5) is 1.0, 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 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 uses arbitrary-precision arithmetic for all integer operations. The Decimal type/class in the decimal module provides decimal floating-point numbers to a pre-defined arbitrary precision and several rounding modes. The Fraction class in the fractions module provides arbitrary precision for
rational number In mathematics, a rational number is a number that can be expressed as the quotient or fraction of two integers, a numerator and a non-zero denominator . For example, is a rational number, as is every integer (e.g. ). The set of all ra ...
s. 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.


Programming examples

Hello world program: print('Hello, world!') Program to calculate the factorial of a positive integer: n = int(input('Type a number, and its factorial will be printed: ')) if n < 0: raise ValueError('You must enter a non-negative integer') factorial = 1 for i in range(2, n + 1): factorial *= i print(factorial)


Libraries

Python's large standard library provides 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 as MIME and
HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...
are supported. It includes modules for creating
graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, ins ...
s, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals, manipulating regular expressions, and unit testing. Some parts of the standard library are covered by specifications—for example, the
Web Server Gateway Interface The Web Server Gateway Interface (WSGI, pronounced ''whiskey'' or ) is a simple calling convention for web servers to forward requests to web applications or frameworks written in the Python programming language. The current version of WSGI, ...
(WSGI) implementation wsgiref follows PEP 333—but most are specified by their code, internal documentation, and test suites. However, because most of the standard library is cross-platform Python code, only a few modules need altering or rewriting for variant implementations. the Python Package Index (PyPI), the official repository for third-party Python software, contains over 415,000 packages with a wide range of functionality, including:


Development environments

Most Python implementations (including CPython) include a read–eval–print loop (REPL), permitting them to function as a command line interpreter for which users enter statements sequentially and receive results immediately. Python also comes with an Integrated development environment (IDE) called IDLE, which is more beginner-oriented. Other shells, including IDLE and IPython, add further abilities such as improved auto-completion, session state retention, and syntax highlighting. As well as standard desktop
integrated development environment An integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of at least a source code editor, build automation tools ...
s, there are
Web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used o ...
-based IDEs, including SageMath, for developing science- and math-related programs; PythonAnywhere, a browser-based IDE and hosting environment; and Canopy IDE, a commercial IDE emphasizing
scientific computing Computational science, also known as scientific computing or scientific computation (SC), is a field in mathematics that uses advanced computing capabilities to understand and solve complex problems. It is an area of science that spans many disc ...
.


Implementations


Reference implementation

CPython is the reference implementation of Python. It is written in C, meeting the C89 standard (Python 3.11 uses C11) with several select C99 features (With later C versions out, it is considered outdated. CPython includes its own C extensions, but third-party extensions are not limited to older C versions—e.g. they can be implemented with C11 or C++.) It compiles Python programs into an intermediate
bytecode Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...
which is then executed by its virtual 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 on Windows 7 and 8;
Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was release to manufacturing, released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Wind ...
was supported until Python 3.5) and most modern
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
systems, including macOS (and Apple M1 Macs, since Python 3.9.1, with experimental installer) and unofficial support for e.g. VMS. Platform portability was one of its earliest priorities. (During Python 1 and 2 development, even OS/2 and Solaris were supported, but support has since been dropped for many platforms.)


Other implementations

* PyPy is a fast, compliant interpreter of Python 2.7 and 3.8. Its
just-in-time compiler In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may c ...
often brings a significant speed improvement over CPython but some libraries written in C cannot be used with it. * Stackless Python is a significant fork of CPython that implements microthreads; it does not use the
call stack In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, program stack, control stack, run-time stack, or mac ...
in the same way, thus allowing massively concurrent programs. PyPy also has a stackless version. * MicroPython and CircuitPython are Python 3 variants optimized for microcontrollers, including Lego 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-time
JIT Jit (also known as jiti, jit-jive and the Harare beat) is a style of popular Zimbabwean dance music. It features a swift rhythm played on drums and accompanied by a guitar. Jit evolved out many diverse influences, including domestic chimurenga, ...
, and an experimental bytecode compiler.


Unsupported implementations

Other just-in-time Python compilers have been developed, but are now unsupported: * Google began a project named Unladen Swallow in 2009, with the aim of speeding up the Python interpreter fivefold by using the
LLVM LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture. LLVM is designed around a language-independent intermediate repre ...
, and of improving its multithreading ability to scale to thousands of cores, while ordinary implementations suffer from the global interpreter lock. * Psyco is a discontinued 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 type In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allowed operations on it. A data type tells the compiler or interpreter how the programmer intends to use the data. Most progra ...
s and is faster than the standard Python code. Psyco does not support Python 2.7 or later. * PyS60 was a Python 2 interpreter for Series 60 mobile phones released by
Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finland, i ...
in 2005. It implemented many of the modules from the standard library and some additional modules for integrating with the Symbian operating system. The Nokia N900 also supports Python with GTK widget libraries, enabling programs to be written and run on the target device.


Cross-compilers to other languages

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: * Brython, Transcrypt and Pyjs (latest release in 2012) compile Python to
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
. * Cython compiles (a superset of) Python 2.7 to C (while the resulting code is also usable with Python 3 and also e.g. C++). * Nuitka compiles Python into C. * Numba uses LLVM to compile a subset of Python to machine code. * Pythran compiles a subset of Python 3 to C++ (
C++11 C11, C.XI, C-11 or C.11 may refer to: Transport * C-11 Fleetster, a 1920s American light transport aircraft for use of the United States Assistant Secretary of War * Fokker C.XI, a 1935 Dutch reconnaissance seaplane * LET C-11, a license-build ...
). * RPython can be compiled to C, and is used to build the PyPy interpreter of Python. * The Python → 11l → C++ transpiler compiles a subset of Python 3 to C++ ( C++17). Specialized: * MyHDL is a Python-based hardware description language (HDL), that converts MyHDL code to Verilog or VHDL code. Older projects (or not to be used with Python 3.x and latest syntax): * Google's Grumpy (latest release in 2017) transpiles Python 2 to Go. * IronPython allows running Python 2.7 programs (and an alpha, released in 2021, is also available for "Python 3.4, although features and behaviors from later versions may be included") on the .NET Common Language Runtime. * Jython compiles Python 2.7 to Java bytecode, allowing the use of the Java libraries from a Python program. * Pyrex (latest release in 2010) and Shed 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 by The Computer Language Benchmarks Game.


Development

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 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 the Roundup bug tracker hosted at by the foundation. In 2022, all issues and discussions were migrated to
GitHub GitHub, Inc. () is an Internet hosting service for software development and version control using Git. It provides the distributed version control of Git plus access control, bug tracking, software feature requests, task management, cont ...
. Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to
GitHub GitHub, Inc. () is an Internet hosting service for software development and version control using Git. It provides the distributed version control of Git plus access control, bug tracking, software feature requests, task management, cont ...
in 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 manually ported. 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. Many alpha, beta, and release-candidates are 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 large unit test suite during development. The major
academic conference An academic conference or scientific conference (also congress, symposium, workshop, or meeting) is an event for researchers (not necessarily academics) to present and discuss their scholarly work. Together with academic or scientific journal ...
on Python is PyCon. There are also special Python mentoring programs, such as Pyladies. Python 3.10 deprecated wstr (to be removed in Python 3.12; meaning Python extensions need to be modified by then), and added pattern matching to the language.


API documentation generators

Tools that can generate documentation for Python API include pydoc (available as part of the standard library), Sphinx, Pdoc and its forks, Doxygen and Graphviz, among others.


Naming

Python's name is derived from the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. 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''. The official Python documentation also contains various references to Monty Python routines. The prefix ''Py-'' is used to show that something is related to Python. 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.


Popularity

Since 2003, Python has consistently ranked in the top ten most popular programming languages in the TIOBE Programming Community Index where, , it is the most popular language (ahead of
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
, and C). It was selected Programming Language of the Year (for "the highest rise in ratings in a year") in 2007, 2010, 2018, and 2020 (the only language to do so four times). 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++". Large organizations that use Python include
Wikipedia Wikipedia is a multilingual free online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and using a wiki-based editing system. Wikipedia is the largest and most-read refer ...
,
Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...
, Yahoo!, CERN,
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
,
Facebook Facebook is an online social media and social networking service owned by American company Meta Platforms. Founded in 2004 by Mark Zuckerberg with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dust ...
,
Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technolog ...
, Instagram,
Spotify Spotify (; ) is a proprietary Swedish audio streaming and media services provider founded on 23 April 2006 by Daniel Ek and Martin Lorentzon. It is one of the largest music streaming service providers, with over 456 million monthly active use ...
, and some smaller entities like ILM and
ITA Ita or ITA may refer to : Places and jurisdictions * ITA, ISO 3166-1 country code for Italy * Ita (Africa), an ancient city and former bishopric in Roman Mauretania, presently a Latin Catholic titular see * Itá, Paraguay People * Ita (pr ...
. The social news networking site Reddit was written mostly in Python.


Uses

Python can serve as a
scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
for
web application A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection. History In earlier computing models like client-serv ...
s, e.g., via for the Apache webserver. With
Web Server Gateway Interface The Web Server Gateway Interface (WSGI, pronounced ''whiskey'' or ) is a simple calling convention for web servers to forward requests to web applications or frameworks written in the Python programming language. The current version of WSGI, ...
, a standard API has evolved to facilitate these applications. Web frameworks like Django,
Pylons Pylon may refer to: Structures and boundaries * Pylon (architecture), the gateway to the inner part of an Ancient Egyptian temple or Christian cathedral * Pylon, a support tower structure for suspension bridges or highways * Pylon, an orange mar ...
,
Pyramid A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilate ...
, TurboGears, web2py,
Tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alt ...
, Flask, Bottle, and Zope support developers in the design and maintenance of complex applications. Pyjs and IronPython can be used to develop the client-side of Ajax-based applications. SQLAlchemy can be used as a data mapper to a relational database. Twisted is a framework to program communications between computers, and is used (for example) by Dropbox. 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. SageMath is a
computer algebra system A computer algebra system (CAS) or symbolic algebra system (SAS) is any mathematical software with the ability to manipulate mathematical expressions in a way similar to the traditional manual computations of mathematicians and scientists. The ...
with a notebook interface programmable in Python: its library covers many aspects of
mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
, including
algebra Algebra () is one of the broad areas of mathematics. Roughly speaking, algebra is the study of mathematical symbols and the rules for manipulating these symbols in formulas; it is a unifying thread of almost all of mathematics. Elementary ...
, combinatorics,
numerical mathematics Numerical analysis is the study of algorithms that use numerical approximation (as opposed to symbolic manipulations) for the problems of mathematical analysis (as distinguished from discrete mathematics). It is the study of numerical methods t ...
, number theory, and
calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematics, mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizati ...
. OpenCV has Python bindings with a rich set of features for computer vision and image processing. Python is commonly used in
artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech ...
projects and machine learning projects with the help of libraries like TensorFlow, Keras, Pytorch, and scikit-learn. As a scripting language with a
modular architecture Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a sy ...
, simple syntax, and rich text processing tools, Python is often used for natural language processing. Python can also be used to create games, with libraries such as Pygame, which can make 2D games. Python has been successfully embedded in many software products as a scripting language, including in finite element method software such as Abaqus, 3D parametric modelers like FreeCAD, 3D animation packages such as
3ds Max Autodesk 3ds Max, formerly 3D Studio and 3D Studio Max, is a professional 3D computer graphics program for making 3D animations, models, games and images. It is developed and produced by Autodesk Media and Entertainment. It has modeling capab ...
, Blender,
Cinema 4D Cinema 4D is a 3D software suite developed by the German company Maxon. Overview As of R21, only one version of Cinema 4D is available. It replaces all previous variants, including BodyPaint 3D, and includes all features of the past 'Studio' ...
, Lightwave,
Houdini Harry Houdini (, born Erik Weisz; March 24, 1874 – October 31, 1926) was a Hungarian-American escape artist, magic man, and stunt performer, noted for his escape acts. His pseudonym is a reference to his spiritual master, French magician ...
, Maya, modo, MotionBuilder,
Softimage Autodesk Softimage, or simply Softimage () was a 3D computer graphics application, for producing 3D computer graphics, 3D modeling, and computer animation. Now owned by Autodesk and formerly titled Softimage, XSI, the software has been predomina ...
, the visual effects compositor Nuke, 2D imaging programs like GIMP, Inkscape, Scribus and Paint Shop Pro, and musical notation programs like scorewriter and capella. GNU Debugger uses Python as a pretty printer to show complex structures such as C++ containers. Esri promotes Python as the best choice for writing scripts in ArcGIS. It has also been used in several video games, and has been adopted as first of the three available
programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...
s in
Google App Engine Google App Engine (often referred to as GAE or simply App Engine) is a cloud computing platform as a service for developing and hosting web applications in Google-managed data centers. Applications are sandboxed and run across multiple servers ...
, the other two being
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
and Go. Many operating systems include Python as a standard component. It ships with most Linux distributions, AmigaOS 4 (using Python 2.7), FreeBSD (as a package), NetBSD, and OpenBSD (as a package) and can be used from the command line (terminal). Many Linux distributions use installers written in Python: Ubuntu uses the Ubiquity installer, while
Red Hat Linux Red Hat Linux was a widely used commercial open-source Linux distribution created by Red Hat until its discontinuation in 2004. Early releases of Red Hat Linux were called Red Hat Commercial Linux. Red Hat published the first non-beta releas ...
and Fedora Linux use the
Anaconda Anacondas or water boas are a group of large snakes of the genus '' Eunectes''. They are found in tropical South America. Four species are currently recognized. Description Although the name applies to a group of snakes, it is often used t ...
installer. Gentoo Linux uses Python in its
package management system A package manager or package-management system is a collection of software tools that automates the process of installing, upgrading, configuring, and removing computer programs for a computer in a consistent manner. A package manager deals w ...
, Portage. Python is used extensively in the
information security Information security, sometimes shortened to InfoSec, is the practice of protecting information by mitigating information risks. It is part of Risk management information systems, information risk management. It typically involves preventing or re ...
industry, including in exploit development. Most of the
Sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or do ...
software for the One Laptop per Child XO, developed at Sugar Labs since 2008, is written in Python. The Raspberry Pi single-board computer project has adopted Python as its main user-programming language. LibreOffice includes Python and intends to replace Java with Python. Its Python Scripting Provider is a core feature since Version 4.0 from 7 February 2013.


Languages influenced by Python

Python's design and philosophy have influenced many other programming languages: * Boo uses indentation, a similar syntax, and a similar object model. * Cobra uses indentation and a similar syntax, and its ''Acknowledgements'' document lists Python first among languages that influenced it. * CoffeeScript, a programming language that cross-compiles to JavaScript, has Python-inspired syntax. *
ECMAScript ECMAScript (; ES) is a JavaScript standard intended to ensure the interoperability of web pages across different browsers. It is standardized by Ecma International in the documenECMA-262 ECMAScript is commonly used for client-side scripti ...
/
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
borrowed iterators and generators from Python. * GDScript, a scripting language very similar to Python, built-in to the Godot game engine. * Go is designed for the "speed of working in a dynamic language like Python" and shares the same syntax for slicing arrays. * Groovy was motivated by the desire to bring the Python design philosophy to
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
. * Julia was designed to be "as usable for general programming as Python". * Nim uses indentation and similar syntax. *
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...
'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. 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 in Tcl, 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

* * * *


Further reading

* * * * * * * Ramalho, Luciano (May 2022).
Fluent Python
' (2nd ed.). O'Reilly Media.
ISBN The International Standard Book Number (ISBN) is a numeric commercial book identifier that is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each separate edition a ...
978-1-4920-5632-4.


External links

* Articles with example Python (programming language) code Class-based programming languages Notebook interface Computer science in the Netherlands Concurrent programming languages Cross-platform free software Cross-platform software Dutch inventions Dynamically typed programming languages Educational programming languages High-level programming languages Information technology in the Netherlands Multi-paradigm programming languages Object-oriented programming languages Pattern matching programming languages Programming languages Programming languages created in 1991 Scripting languages Text-oriented programming languages {{Good article