GitHub - PythonCharmers/python-future: Easy, clean, reliable Python 2/3 compatibility (original) (raw)

Overview: Easy, clean, reliable Python 2/3 compatibility

python-future is the missing compatibility layer between Python 2 and Python 3. It allows you to use a single, clean Python 3.x-compatible codebase to support both Python 2 and Python 3 with minimal overhead.

It provides future and past packages with backports and forward ports of features from Python 3 and 2. It also comes with futurize andpasteurize, customized 2to3-based scripts that helps you to convert either Py2 or Py3 code easily to support both Python 2 and 3 in a single clean Py3-style codebase, module by module.

The python-future project has been downloaded over 1.7 billion times.

Status

The python-future project was created in 2013 to attempt to save Python from the schism of version incompatibility that was threatening to tear apart the language (as Perl 6 contributed to the death of Perl).

That time is now past. Thanks to a huge porting effort across the Python community, Python 3 eventually thrived. Python 2 reached its end of life in 2020 and the python-future package should no longer be necessary. Use it to help with porting legacy code to Python 3 but don't depend on it for new code.

Features

• future.builtins package (also available as builtins on Py2) provides backports and remappings for 20 builtins with different semantics on Py3 versus Py2
• support for directly importing 30 standard library modules under their Python 3 names on Py2
• support for importing the other 14 refactored standard library modules under their Py3 names relatively cleanly viafuture.standard_library and future.moves
• past.builtins package provides forward-ports of 19 Python 2 types and builtin functions. These can aid with per-module code migrations.
• past.translation package supports transparent translation of Python 2 modules to Python 3 upon import. [This feature is currently in alpha.]
• 1000+ unit tests, including many from the Py3.3 source tree.
• futurize and pasteurize scripts based on 2to3 and parts of3to2 and python-modernize, for automatic conversion from either Py2 or Py3 to a clean single-source codebase compatible with Python 2.6+ and Python 3.3+.
• a curated set of utility functions and decorators in future.utils andpast.utils selected from Py2/3 compatibility interfaces from projects like six, IPython, Jinja2, Django, and Pandas.
• support for the surrogateescape error handler when encoding and decoding the backported str and bytes objects. [This feature is currently in alpha.]
• support for pre-commit hooks

Code examples

Replacements for Py2's built-in functions and types are designed to be imported at the top of each Python module together with Python's built-in __future__statements. For example, this code behaves identically on Python 2.6/2.7 after these imports as it does on Python 3.3+:

from future import absolute_import, division, print_function from builtins import (bytes, str, open, super, range, zip, round, input, int, pow, object)

Backported Py3 bytes object

b = bytes(b'ABCD') assert list(b) == [65, 66, 67, 68] assert repr(b) == "b'ABCD'"

These raise TypeErrors:

b + u'EFGH'

bytes(b',').join([u'Fred', u'Bill'])

Backported Py3 str object

s = str(u'ABCD') assert s != bytes(b'ABCD') assert isinstance(s.encode('utf-8'), bytes) assert isinstance(b.decode('utf-8'), str) assert repr(s) == "'ABCD'" # consistent repr with Py3 (no u prefix)

These raise TypeErrors:

bytes(b'B') in s

s.find(bytes(b'A'))

Extra arguments for the open() function

f = open('japanese.txt', encoding='utf-8', errors='replace')

New zero-argument super() function:

class VerboseList(list): def append(self, item): print('Adding an item') super().append(item)

New iterable range object with slicing support

for i in range(10**15)[:10]: pass

Other iterators: map, zip, filter

my_iter = zip(range(3), ['a', 'b', 'c']) assert my_iter != list(my_iter)

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() replaces Py2's raw_input() (with no eval()):

name = input('What is your name? ') print('Hello ' + name)

pow() supports fractional exponents of negative numbers like in Py3:

z = pow(-1, 0.5)

Compatible output from isinstance() across Py2/3:

assert isinstance(2**64, int) # long integers assert isinstance(u'blah', str) assert isinstance('blah', str) # only if unicode_literals is in effect

Py3-style iterators written as new-style classes (subclasses of

future.types.newobject) are automatically backward compatible with Py2:

class Upper(object): def init(self, iterable): self._iter = iter(iterable) def next(self): # note the Py3 interface return next(self._iter).upper() def iter(self): return self assert list(Upper('hello')) == list('HELLO')

There is also support for renamed standard library modules. The recommended interface works like this:

Many Py3 module names are supported directly on both Py2.x and 3.x:

from http.client import HttpConnection import html.parser import queue import xmlrpc.client

Refactored modules with clashing names on Py2 and Py3 are supported

as follows:

from future import standard_library standard_library.install_aliases()

Then, for example:

from itertools import filterfalse, zip_longest from urllib.request import urlopen from collections import ChainMap from collections import UserDict, UserList, UserString from subprocess import getoutput, getstatusoutput from collections import Counter, OrderedDict # backported to Py2.6

Automatic conversion to Py2/3-compatible code

python-future comes with two scripts called futurize andpasteurize to aid in making Python 2 code or Python 3 code compatible with both platforms (Py2/3). It is based on 2to3 and uses fixers from lib2to3,lib3to2, and python-modernize, as well as custom fixers.

futurize passes Python 2 code through all the appropriate fixers to turn it into valid Python 3 code, and then adds __future__ and future package imports so that it also runs under Python 2.

For conversions from Python 3 code to Py2/3, use the pasteurize script instead. This converts Py3-only constructs (e.g. new metaclass syntax) to Py2/3 compatible constructs and adds __future__ and future imports to the top of each module.

In both cases, the result should be relatively clean Py3-style code that runs mostly unchanged on both Python 2 and Python 3.

Futurize: 2 to both

For example, running futurize -w mymodule.py turns this Python 2 code:

import Queue from urllib2 import urlopen

def greet(name): print 'Hello', print name

print "What's your name?", name = raw_input() greet(name)

into this code which runs on both Py2 and Py3:

from future import print_function from future import standard_library standard_library.install_aliases() from builtins import input import queue from urllib.request import urlopen

def greet(name): print('Hello', end=' ') print(name)

print("What's your name?", end=' ') name = input() greet(name)

The first four lines have no effect under Python 3 and can be removed from the codebase when Python 2 compatibility is no longer required.

See :ref:`forwards-conversion` and :ref:`backwards-conversion` for more details.

Automatic translation

The past package can automatically translate some simple Python 2 modules to Python 3 upon import. The goal is to support the "long tail" of real-world Python 2 modules (e.g. on PyPI) that have not been ported yet. For example, here is how to use a Python 2-only package called plotrique on Python 3. First install it:

$ pip3 install plotrique==0.2.5-7 --no-compile # to ignore SyntaxErrors

(or use pip if this points to your Py3 environment.)

Then pass a whitelist of module name prefixes to the autotranslate() function. Example:

$ python3

from past.translation import autotranslate autotranslate(['plotrique']) import plotrique

This transparently translates and runs the plotrique module and any submodules in the plotrique package that plotrique imports.

This is intended to help you migrate to Python 3 without the need for all your code's dependencies to support Python 3 yet. It should be used as a last resort; ideally Python 2-only dependencies should be ported properly to a Python 2/3 compatible codebase using a tool likefuturize and the changes should be pushed to the upstream project.

Note: the auto-translation feature is still in alpha; it needs more testing and development, and will likely never be perfect.

Pre-commit hooks

Pre-commit is a framework for managing and maintaining multi-language pre-commit hooks.

In case you need to port your project from Python 2 to Python 3, you might consider using such hook during the transition period.

First:

and then in your project's directory:

Next, you need to add this entry to your .pre-commit-config.yaml

• repo: https://github.com/PythonCharmers/python-future rev: master hooks: - id: futurize args: [--both-stages]

The args part is optional, by default only stage1 is applied.

Licensing

Docs

See the docs here.

Next steps

If you are new to Python-Future, check out the Quickstart Guide.

For an update on changes in the latest version, see the What's New page.