Clean single-source support for Python 3 and 2
The future module helps run Python 3.x-compatible code under Python 2 with minimal code cruft.
The goal is to allow you to write clean, modern, forward-compatible Python 3 code today and to run it with minimal effort under Python 2 alongside a Python 2 stack that may contain dependencies that have not yet been ported to Python 3.
It is designed to be used as follows:
from __future__ import (division, absolute_import, print_function, unicode_literals) from future import *
followed by clean Python 3 code (with a few restrictions) that can run unchanged on Python 2.7.
On Python 3, the from future import * line has no effect (i.e. zero namespace pollution.) On Python 2 it shadows builtins to provide the Python 3 semantics. (See below for the explicit import form.)
After the imports, this code runs identically on Python 3 and 2:
# New iterable range object with slicing support for i in range(10**11)[:10]: pass # Other common iterators: map, reduce, zip my_iter = zip(range(3), ['a', 'b', 'c']) assert my_iter != list(my_iter) # New simpler super() function: class VerboseList(list): def append(self, item): print('Adding an item') super().append(item) # These raise NameErrors: # apply(), cmp(), coerce(), reduce(), xrange(), etc. # This identity is restored. This is normally valid on Py3 and Py2, but # 'from __future__ import unicode_literals' breaks it on Py2: assert isinstance('happy', str) # The round() function behaves as it does in Python 3, using "Banker's # Rounding" to the nearest even last digit: assert round(0.1250, 2) == 0.12 # input() is now safe (no eval()): name = input('What is your name? ') print('Hello ' + name)
future also supports the standard library reorganization (PEP 3108) via import hooks, allowing standard library modules to be accessed under their Python 3 names and locations:
from future import standard_library import socketserver import queue import configparser import test.support from collections import UserList from itertools import filterfalse, zip_longest # and other moved modules and definitions
It also includes backports for these stdlib packages from Py3 that were heavily refactored versus Py2:
import html, html.entities, html.parser import http, http.client
These currently are not supported, but we may support them in the future:
import http.server, http.cookies, http.cookiejar import urllib, urllib.parse, urllib.request, urllib.error
If you prefer explicit imports, the explicit equivalent of the from future import * line above is:
from future.common_iterators import zip, map, filter from future.builtins import ascii, oct, hex, chr from future.modified_builtins import (range, super, round, input) from future.disable_obsolete_builtins import (apply, cmp, coerce, execfile, file, long, raw_input, reduce, reload, unicode, xrange, StandardError) from future.str_is_unicode import str
But please note that the API is still evolving rapidly.
See the docstrings for each of these modules for more info:
- future.standard_library - future.common_iterators - future.builtins - future.modified_builtins - future.disable_obsolete_builtins - future.str_as_unicode
An experimental script called python-futurize is included to aid in making either Python 2 code or Python 3 code compatible with both platforms using the future module. See https://github.com/edschofield/python-future#automatic-conversion.
|Sponsor:||Python Charmers Pty Ltd, Australia, and Python Charmers Pte Ltd, Singapore. http://pythoncharmers.com|
|Others:||The super() and range() functions are derived from Ryan Kelly’s magicsuper module and Dan Crosta’s xrange module. The python_2_unicode_compatible decorator is from django.utils.encoding. The fix_metaclass 2to3 fixer (from Armin Ronacher’s python-modernize) was authored by Jack Diederich and Daniel Neuhaeuser.|
Copyright 2013 Python Charmers Pty Ltd, Australia. The software is distributed under an MIT licence. See LICENSE.txt.