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.. _quickstart-guide:
Quick-start guide
=================
You can use ``future`` to help to port your code from Python 2 to Python 3
today -- and still have it run on Python 2.
If you already have Python 3 code, you can instead use ``future`` to
offer Python 2 compatibility with almost no extra work.
Installation
------------
To install the latest stable version, type::
pip install future
If you would prefer the latest development version, it is available `here
<https://github.com/PythonCharmers/python-future>`_.
If you are writing code from scratch
------------------------------------
The easiest way is to start each new module with these lines::
from __future__ import (absolute_import, division,
print_function, unicode_literals)
from builtins import *
Then write standard Python 3 code. The :mod:`future` package will
provide support for running your code on Python 2.7, and 3.4+ mostly
unchanged.
- For explicit import forms, see :ref:`explicit-imports`.
- For more details, see :ref:`what-else`.
- For a cheat sheet, see :ref:`compatible-idioms`.
To convert existing Python 3 code
---------------------------------
To offer backward compatibility with Python 2 from your Python 3 code,
you can use the ``pasteurize`` script. This adds these lines at the top of each
module::
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals
from builtins import open
from builtins import str
# etc., as needed
from future import standard_library
standard_library.install_aliases()
and converts several Python 3-only constructs (like keyword-only arguments) to a
form compatible with both Py3 and Py2. Most remaining Python 3 code should
simply work on Python 2.
See :ref:`backwards-conversion` for more details.
To convert existing Python 2 code
---------------------------------
.. include:: futurize_overview.rst
See :ref:`forwards-conversion-stage1` and :ref:`forwards-conversion-stage2` for more details.
.. If you already know Python 3, start with the :ref:`automatic-conversion` page.
.. If you don't know Python 3 yet, start with :ref:`python3-essentials`.
.. _standard-library:
Standard library reorganization
-------------------------------
:mod:`future` supports the standard library reorganization (PEP 3108) via
one of several mechanisms, allowing most moved standard library modules
to be accessed under their Python 3 names and locations in Python 2::
from future import standard_library
standard_library.install_aliases()
# Then these Py3-style imports work on both Python 2 and Python 3:
import socketserver
import queue
from collections import UserDict, UserList, UserString
from collections import ChainMap # even on Py2.7
from itertools import filterfalse, zip_longest
import html
import html.entities
import html.parser
import http
import http.client
import http.server
import http.cookies
import http.cookiejar
import urllib.request
import urllib.parse
import urllib.response
import urllib.error
import urllib.robotparser
import xmlrpc.client
import xmlrpc.server
and others. For a complete list, see :ref:`direct-imports`.
.. _py2-dependencies:
Python 2-only dependencies
--------------------------
If you have dependencies that support only Python 2, you may be able to use the
``past`` module to automatically translate these Python 2 modules to Python 3
upon import. First, install the Python 2-only package into your Python 3
environment::
$ pip3 install mypackagename --no-compile # to ignore SyntaxErrors
(or use ``pip`` if this points to your Py3 environment.)
Then add the following code at the top of your (Py3 or Py2/3-compatible)
code::
from past.translation import autotranslate
autotranslate(['mypackagename'])
import mypackagename
This feature is experimental, and we would appreciate your feedback on
how well this works or doesn't work for you. Please file an issue `here
<https://github.com/PythonCharmers/python-future>`_ or post to the
`python-porting <https://mail.python.org/mailman/listinfo/python-porting>`_
mailing list.
For more information on the automatic translation feature, see :ref:`translation`.
Next steps
----------
For more information about writing Py2/3-compatible code, see:
- :ref:`compatible-idioms`
- :ref:`what-else`.
|
