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Link py2 docs to py3 docs. Fix invisible subheading. Note that pip is part of the Python install now; closes #347. Suggest avoiding eol 2.6 unless paid specifically.
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6.2 KiB
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156 lines
6.2 KiB
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Picking an Python Interpreter (3 vs. 2)
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=======================================
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.. image:: https://farm5.staticflickr.com/4265/34484834733_5b80f65ab1_k_d.jpg
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.. _which-python:
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The State of Python (3 & 2)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When choosing a Python interpreter, one looming question is always present:
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"Should I choose Python 2 or Python 3"? The answer is a bit more subtle than
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one might think.
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The basic gist of the state of things is as follows:
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1. Most production applications today use Python 2.7.
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2. Python 3 is ready for the production deployment of applications today.
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3. Python 2.7 will only receive necessary security updates until 2020 [#pep373_eol]_.
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4. The brand name "Python" encapsulates both Python 3 and Python 2.
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Recommendations
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~~~~~~~~~~~~~~~
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.. note:: The use of **Python 3** is *highly* preferred over Python 2. Consider upgrading your applications and infrastructure if you find yourself *still* using Python 2 in production today. If you are using Python 3, congratulations — you are indeed a person of excellent taste.
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—*Kenneth Reitz*
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I'll be blunt:
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- Use Python 3 for new Python applications.
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- If you're learning Python for the first time, familiarizing yourself with Python 2.7 will be very
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useful, but not more useful than learning Python 3.
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- Learn both. They are both "Python".
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- Software that is already built often depends on Python 2.7.
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- If you are writing a new open source Python library, it's best to write it for both Python 2 and 3
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simultaneously. Only supporting Python 3 for a new library you want to be widely adopted is a
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political statement and will alienate many of your users. This is not a problem — slowly, over the next three years, this will become less the case.
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So.... 3?
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~~~~~~~~~
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If you're choosing a Python interpreter to use, I
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recommend you use the newest Python 3.x, since every version brings new and
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improved standard library modules, security and bug fixes.
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Given such, only use Python 2 if you have a strong reason to, such as a
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pre-existing code-base, a Python 2 exclusive library, simplicity/familiarity,
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or, of course, you absolutely love and are inspired by Python 2. No harm in that.
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Check out `Can I Use Python 3? <https://caniusepython3.com/>`_ to see if any
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software you're depending on will block your adoption of Python 3.
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`Further Reading <http://wiki.python.org/moin/Python2orPython3>`_
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It is possible to `write code that works on Python 2.6, 2.7, and Python 3
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<https://docs.python.org/3/howto/pyporting.html>`_. This
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ranges from trivial to hard depending upon the kind of software
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you are writing; if you're a beginner there are far more important things to
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worry about. Note that Python 2.6 is end-of-life upstream, so you shouldn't
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try to write 2.6-compatible code unless you're being paid specifically to
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do that.
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Implementations
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~~~~~~~~~~~~~~~
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When people speak of *Python* they often mean not just the language but also
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the CPython implementation. *Python* is actually a specification for a language
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that can be implemented in many different ways.
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CPython
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-------
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`CPython <http://www.python.org>`_ is the reference implementation of Python,
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written in C. It compiles Python code to intermediate bytecode which is then
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interpreted by a virtual machine. CPython provides the highest
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level of compatibility with Python packages and C extension modules.
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If you are writing open-source Python code and want to reach the widest possible
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audience, targeting CPython is best. To use packages which rely on C extensions
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to function, CPython is your only implementation option.
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All versions of the Python language are implemented in C because CPython is the
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reference implementation.
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PyPy
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----
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`PyPy <http://pypy.org/>`_ is a Python interpreter implemented in a restricted
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statically-typed subset of the Python language called RPython. The interpreter
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features a just-in-time compiler and supports multiple back-ends (C, CLI, JVM).
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PyPy aims for maximum compatibility with the reference CPython implementation
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while improving performance.
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If you are looking to increase performance of your Python code, it's
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worth giving PyPy a try. On a suite of benchmarks, it's currently `over 5 times
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faster than CPython <http://speed.pypy.org/>`_.
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PyPy supports Python 2.7. PyPy3 [#pypy_ver]_, released in beta, targets Python 3.
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Jython
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------
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`Jython <http://www.jython.org/>`_ is a Python implementation that compiles
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Python code to Java bytecode which is then executed by the JVM (Java Virtual Machine).
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Additionally, it is able to import and use any Java class like a Python
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module.
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If you need to interface with an existing Java codebase or have other reasons to
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need to write Python code for the JVM, Jython is the best choice.
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Jython currently supports up to Python 2.7. [#jython_ver]_
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IronPython
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----------
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`IronPython <http://ironpython.net/>`_ is an implementation of Python for the .NET
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framework. It can use both Python and .NET framework libraries, and can also
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expose Python code to other languages in the .NET framework.
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`Python Tools for Visual Studio <http://ironpython.net/tools/>`_ integrates
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IronPython directly into the Visual Studio development environment, making it
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an ideal choice for Windows developers.
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IronPython supports Python 2.7. [#iron_ver]_
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PythonNet
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---------
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`Python for .NET <http://pythonnet.github.io/>`_ is a package which
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provides near seamless integration of a natively installed Python
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installation with the .NET Common Language Runtime (CLR). This is the
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inverse approach to that taken by IronPython (see above), to which it
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is more complementary than competing with.
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In conjunction with Mono, pythonnet enables native Python
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installations on non-Windows operating systems, such as OS X and
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Linux, to operate within the .NET framework. It can be run in
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addition to IronPython without conflict.
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Pythonnet supports from Python 2.6 up to Python 3.5. [#pythonnet_ver1]_ [#pythonnet_ver2]_
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.. [#pypy_ver] http://pypy.org/compat.html
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.. [#jython_ver] https://hg.python.org/jython/file/412a8f9445f7/NEWS
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.. [#iron_ver] http://ironpython.codeplex.com/releases/view/81726
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.. [#pythonnet_ver1] https://travis-ci.org/pythonnet/pythonnet
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.. [#pythonnet_ver2] https://ci.appveyor.com/project/TonyRoberts/pythonnet-480xs
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.. [#pep373_eol] https://www.python.org/dev/peps/pep-0373/#id2
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