|Usual file extensions||.py, .pyw, .pyc, .pyo, .pyd|
|Paradigm||multi-paradigm: object-oriented, imperative, functional, reflective|
|Designed by||Guido van Rossum|
|Developer||Python Software Foundation|
|Stable release||3.1.1/ August 17, 2009
2.6.4/ October 25, 2009
|Preview release||2.7 alpha 3 / February 6, 2010|
|Typing discipline||duck, dynamic, strong|
|Major implementations||CPython, IronPython, Jython, Python for S60, PyPy, Unladen Swallow|
|Dialects||Stackless Python, RPython|
|Influenced by||ABC, ALGOL 68, C, Haskell, Icon, Lisp, Modula-3, Perl, Java|
|Influenced||Boo, Cobra, D, Dao, Falcon, Groovy, Nimrod, Ruby|
|License||Python Software Foundation License|
Python is a general-purpose high-level programming language  whose design philosophy emphasizes code readability. Python aims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive. Its use of indentation for block delimiters is unusual among popular programming languages.
Python supports multiple programming paradigms, primarily object oriented, imperative, and functional, and features a fully dynamic type system and automatic memory management, similar to that of Scheme, Ruby, Perl, and Tcl. Like other dynamic languages, Python is often used as a scripting language, but is also used in a wide range of non-scripting contexts.
The reference implementation of Python (CPython) has an open, community-based development model, as do all or nearly all of its alternative implementations. CPython is managed by the non-profit Python Software Foundation.
Python was conceived in the late 1980s and its implementation was started in December 1989 by Guido van Rossum at CWI in the Netherlands as a successor to the ABC programming language (itself inspired by SETL) capable of exception handling and interfacing with the Amoeba operating system. Van Rossum is Python's principal author, and his continuing central role in deciding the direction of Python is reflected in the title given to him by the Python community, Benevolent Dictator for Life (BDFL).
Python 2.0 was released on 16 October 2000, with many major new features including a full garbage collector and support for Unicode. However, the most important change was to the development process itself, with a shift to a more transparent and community-backed process. Python 3.0, a major, backwards-incompatible release, was released on 3 December 2008 after a long period of testing. Many of its major features have been backported to the backwards-compatible Python 2.6.
Python is a multi-paradigm programming language. Rather than forcing programmers to adopt a particular style of programming, it permits several styles: object-oriented programming and structured programming are fully supported, and there are a number of language features which support functional programming and aspect-oriented programming (including by metaprogramming and by magic methods). Many other paradigms are supported using extensions, such as pyDBC and Contracts for Python which allow Design by Contract.
Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management. An important feature of Python is dynamic name resolution (late binding), which binds method and variable names during program execution.
Rather than requiring all desired functionality to be built into the language's core, Python was designed to be highly extensible. New built-in modules can be easily written in C, C++ or Cython. Python can also be used as an extension language for existing modules and applications that need a programmable interface. This design of a small core language with a large standard library and an easily extensible interpreter was intended by Van Rossum from the very start because of his frustrations with ABC (which espoused the opposite mindset).
The design of Python offers only limited support for functional programming in the Lisp tradition. However, Python's design philosophy exhibits significant similarities to those of minimalist Lisp-family languages, such as Scheme. The library has two modules (itertools and functools) that implement proven functional tools borrowed from Haskell and Standard ML.
While offering choice in coding methodology, the Python philosophy rejects exuberant syntax, such as in Perl, in favor of a sparser, less-cluttered grammar. Python's developers expressly promote a particular "culture" or ideology based on what they want the language to be, favoring language forms they see as "beautiful", "explicit" and "simple". As Alex Martelli put it in his Python Cookbook (2nd ed., p. 230): "To describe something as clever is NOT considered a compliment in the Python culture." Python's philosophy rejects the Perl "there is more than one way to do it" approach to language design in favor of "there should be one—and preferably only one—obvious way to do it".
Python's developers eschew premature optimization, and moreover, reject patches to non-critical parts of CPython which would offer a marginal increase in speed at the cost of clarity. It is sometimes described as "slow". However, by the Pareto principle, most problems and sections of programs are not speed critical. When speed is a problem, Python programmers tend to try to optimize bottlenecks by algorithm improvements or data structure changes, using a JIT compiler such as Psyco, rewriting the time-critical functions in "closer to the metal" languages such as C, or by translating (a dialect of) Python code to C code using tools like Cython.
The core philosophy of the language is summarized by the document "PEP 20 (The Zen of Python)".
A common neologism in the Python community is pythonic, which can have a wide range of meanings related to program style. To say that a piece of code is pythonic is to say that it uses Python idioms well, that it is natural or shows fluency in the language. Likewise, to say of an interface or language feature that it is pythonic is to say that it works well with Python idioms, that its use meshes well with the rest of the language.
In contrast, a mark of unpythonic code is that it attempts to write C++ (or Lisp, Perl, or Java) code in Python—that is, provides a rough transcription rather than an idiomatic translation of forms from another language. The concept of pythonicity is tightly bound to Python's minimalist philosophy of readability and avoiding the "there's more than one way to do it" approach. Unreadable code or incomprehensible idioms are unpythonic.
Users and admirers of Python—most especially those considered knowledgeable or experienced—are often referred to as Pythonists, Pythonistas, and Pythoneers.
The prefix Py can be 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); PyS60, an implementation for the Symbian Series 60 Operating System; PyQt and PyGTK, which bind Qt and GTK, respectively, to Python; and PyPy, a Python implementation written in Python. The prefix is also used outside of naming software packages: the major Python conference is named PyCon.
An important goal of the Python developers is making Python fun to use. This is reflected in the origin of the name (based on the television series Monty Python's Flying Circus), in the common practice of using Monty Python references in example code, and in an occasionally playful approach to tutorials and reference materials. For example, the metasyntactic variables often used in Python literature are spam and eggs, instead of the traditional foo and bar.
Python is often used as a scripting language for web applications, e.g. via mod_python for the Apache web server. With Web Server Gateway Interface a standard API has been developed to facilitate these applications. Web application frameworks or application servers like Django, Pylons, TurboGears, web2py and Zope support developers in the design and maintenance of complex applications. Libraries like NumPy, Scipy and Matplotlib allow Python to be used effectively in scientific computing.
Python has been successfully embedded in a number of software products as a scripting language, including in finite element method software such as Abaqus, 3D animation packages such as Maya, MotionBuilder, Softimage, Cinema 4D, BodyPaint 3D, modo, and Blender, and 2D imaging programs like GIMP, Inkscape, Scribus, and Paint Shop Pro. ESRI is now promoting Python as the best choice for writing scripts in ArcGIS. It has even been used in several videogames.
For many operating systems, Python is a standard component; it ships with most Linux distributions, with NetBSD, and OpenBSD, and with Mac OS X. Ubuntu uses the Ubiquity installer, while Red Hat Linux and Fedora use the Anaconda installer, and both installers are written in Python. Gentoo Linux uses Python in its package management system, Portage, and the standard tool to access it, emerge. Pardus uses it for administration and during system boot.
Among the users of Python are YouTube and the original BitTorrent client. Large organizations that make use of Python include Google, Yahoo!, CERN, NASA, and ITA. Most of the Sugar software for the One Laptop Per Child XO, now developed at Sugar Labs, is written in Python.
Python was intended to be a highly readable language. It is designed to have an uncluttered visual layout, frequently using English keywords where other languages use punctuation. Python requires less boilerplate than traditional manifestly typed structured languages such as C or Pascal, and has a smaller number of syntactic exceptions and special cases than either of these.
Python uses whitespace indentation, rather than curly braces or keywords, to delimit blocks (a feature also known as the off-side rule). An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block.
Python's statements include:
ifstatement, which conditionally executes a block of code, along with
elif(a contraction of else-if).
forstatement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block.
whilestatement, which executes a block of code as long as its condition is true.
trystatement, which allows exceptions raised in its attached code block to be caught and handled by
exceptclauses; it also ensures that clean-up code in a
finallyblock will always be run regardless of how the block exits.
classstatement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming.
defstatement, which defines a function or method.
withstatement, which encloses a code block within a context manager (for example, acquiring a lock before the block of code is run, and releasing the lock afterwards).
passstatement, which serves as a NOP and can be used in place of a code block.
Each statement has its own semantics: for example, the
def statement does not execute its block immediately, unlike most other statements.
CPython does not support continuations, and according to Guido van Rossum it never will. However, better support for coroutine-like functionality is provided in 2.5, by extending Python's generators. Prior to 2.5, generators were lazy iterators; information was passed unidirectionally out of the generator. As of Python 2.5, it is possible to pass information back into a generator function.
Methods on objects are functions attached to the object's class; the syntax
instance.method(argument) is, for normal methods and functions, syntactic sugar for
Class.method(instance, argument). Python methods have an explicit
self parameter to access instance data, in contrast to the implicit self in some other object-oriented programming languages (for example, Java, C++ or Ruby).
Python uses duck typing and has typed objects but untyped variable names. Type constraints are not checked at compile time; rather, operations on an object may fail, signifying that the given object is not of a suitable type. Despite being dynamically typed, Python is strongly typed, forbidding operations that are not well-defined (for example, adding a number to a string) rather than silently attempting to make sense of them.
Python allows programmers to define their own types using classes, which are most often used for object-oriented programming. New instances of classes are constructed by calling the class (for example,
EggsClass()), and the classes themselves are instances of the metaclass
type (itself an instance of itself), allowing metaprogramming and reflection.
Prior to version 3.0, Python had two kinds of classes: "old-style" and "new-style". Old-style classes were eliminated in Python 3.0, making all classes new-style. In versions between 2.2 and 3.0, both kinds of classes could be used. The syntax of both styles is the same, the difference being whether the class
object is inherited from, directly or indirectly (all new-style classes inherit from
object and are instances of
Here is a summary of Python's built-in types:
||An immutable sequence of Unicode characters||
||An immutable sequence of bytes||
||Mutable, can contain mixed types||
||Immutable, can contain mixed types||
||Unordered, contains no duplicates||
||A mutable group of key and value pairs||
||An immutable fixed precision number of unlimited magnitude||
||An immutable floating point number (system-defined precision)||
||An immutable complex number with real number and imaginary parts||
||An immutable truth value||
While many programming languages round the result of integer division towards zero, Python always rounds it down towards minus infinity; so that
7//3 is 2, but
(−7)//3 is −3.
Python provides a
round function for rounding floats to integers. Version 2.6.1 and lower use round-away-from-zero:
round(0.5) is 1.0,
round(-0.5) is -1.0. Version 3.0 and higher use round-to-even:
round(1.5) is 2.0,
round(2.5) is 2.0. The
Decimal type/class in module
decimal (since version 2.4) provides exact numerical representation and several rounding modes.
The mainstream Python implementation, known as CPython, is written in C meeting the C89 standard. CPython compiles Python programs into intermediate bytecode, which are then executed by the virtual machine. It is distributed with a large standard library written in a mixture of C and Python. CPython ships in versions for many platforms, including Microsoft Windows and most modern Unix-like systems. CPython was intended from almost its very conception to be cross-platform; its use and development on esoteric platforms such as Amoeba, alongside more conventional ones like Unix and Mac OS, has greatly helped in this regard.
Google started a project called Unladen Swallow in 2009 with the aims of increasing the speed of the Python interpreter by 5 times and improving its multithreading ability to scale to thousands of cores.
In 2005 Nokia released a Python interpreter for the Series 60 mobile phones called PyS60. It includes many of the modules from the CPython implementations and some additional modules for integration with the Symbian operating system. This project has been kept up to date to run on all variants of the S60 platform and there are several third party modules available. The Nokia N900 also supports Python with gtk windows libraries, with the feature that programs can be both written and run on the device itself. There is also a Python interpreter for Windows CE devices (including Pocket PC). It is called PythonCE. There are additional tools available for easy application and GUI development.
ChinesePython (中蟒) is a Python programming language using Chinese language lexicon. Besides reserved words and variable names, most data type operations can be coded in Chinese as well.
Most Python implementations (including CPython, the primary implementation) can function as a command line interpreter, for which the user enters statements sequentially and receives the results immediately. In short, Python acts as a shell. While the semantics of the other modes of execution (bytecode compilation, or compilation to native code) preserve the sequential semantics, they offer a speed boost at the cost of interactivity, so they are usually only used outside of a command-line interaction (eg, when importing a module).
Other shells add capabilities beyond those in the basic interpreter, including IDLE, IPython, and bpython. While generally following the visual style of the Python shell, they implement features like auto-completion, retention of session state, and syntax highlighting.
Some implementations can compile not only to bytecode, but can turn Python code into machine code. So far, this has only been done for restricted subsets of Python. PyPy takes this approach, naming its restricted compilable version of Python RPython.
Psyco is a specialising just in time compiler that integrates with CPython and transforms bytecode to machine code at runtime. The produced code is specialised for certain data types and is faster than standard Python code. Psyco is compatible with all Python code, not only a subset.
Python development is conducted largely through the Python Enhancement Proposal (or "PEP") process. PEPs are standardized design documents providing general information related to Python, including proposals, descriptions, design rationales, and explanations for language features. Outstanding PEPs are reviewed and commented upon by Van Rossum, the Python project's Benevolent Dictator for Life (leader / language architect). CPython's developers also communicate over a mailing list, python-dev, which is the primary forum for discussion about the language's development; specific issues are discussed in the Roundup bug tracker maintained at python.org. Development takes place at the self-hosted svn.python.org.
CPython's public releases come in three types, distinguished by which part of the version number is incremented:
A number of alpha, beta, and release-candidates are also released as previews and for testing before the final release is made. Although there is a rough schedule for each release, this is often pushed back if the code is not ready. The development team monitor the state of the code by running the large unit test suite during development, and using the BuildBot continuous integration system.
Python has a large standard library, commonly cited as one of Python's greatest strengths, providing pre-written tools suited to many tasks. This is deliberate and has been described as a "batteries included" Python philosophy. The modules of the standard library can be augmented with custom modules written in either C or Python. Recently, Boost C++ Libraries includes a library, Boost.Python, to enable interoperability between C++ and Python. Because of the wide variety of tools provided by the standard library, combined with the ability to use a lower-level language such as C and C++, which is already capable of interfacing between other libraries, Python can be a powerful glue language between languages and tools.
The standard library is particularly well tailored to writing Internet-facing applications, with a large number of standard formats and protocols (such as MIME and HTTP) already supported. Modules for creating graphical user interfaces, connecting to relational databases, arithmetic with arbitrary precision decimals, manipulating regular expressions, and doing unit testing are also included.
Some parts of the standard library are covered by specifications (for example, the WSGI implementation
wsgiref follows PEP 333), but the majority of the modules are not. They are specified by their code, internal documentation, and test suite (if supplied). However, because most of the standard library is cross-platform Python code, there are only a few modules that must be altered or completely rewritten by alternative implementations.
Python's design and philosophy have influenced several programming languages, including:
Python's development practices have also been emulated by other languages. The practice of requiring a document describing the rationale for, and issues surrounding, a change to the language (in Python's case, a PEP) is also used in Tcl and Erlang because of Python's influence.
Python is an open source programming language that was made to look good and be easy to read. It was created by a programmer named Guido van Rossum in the year 1991. The language is named after the TV show Monty Python and many examples include jokes from the show.
Python is an interpreted language. An interpreted language allows the programmer to give the source code to the computer and the computer runs the code right away. This means if the programmer needs to change the code they can see the result of any changes quickly. This makes Python a good programming language for beginners and for rapid development because unlike some compiled languages you do not have to go through the Compile-Build-Run-Debug cycle with Python.
Python is a high-level programming language. A high level language has advanced features which allow the programmer to write instructions without having to worry about how the computer is going to carry them out. This makes writing programs easier and faster. Python derives some of its syntax from C and can use modules written in C.
Python is used by hundreds of thousands of programmers and in many application domains. Its rich standard library along thousands of libraries available on the Internet make it a powerful language. The following represents some of its applications:
This is a small example Python program, which defines a function called
hello(), which shows the sentence "I don't like Spam!" to the computer's standard output.
print "I don't like Spam!"