past: an implementation of Python 2 constructs in Python 3

past is a package to aid with Python 2/3 compatibility. Whereas future contains backports of Python 3 constructs to Python 2, past provides implementations of some Python 2 constructs in Python 3. It is intended to be used sparingly, as a way of running old Python 2 code from Python 3 until it is ported properly.

Potential uses for libraries:

• as a step in porting a Python 2 codebase to Python 3 (e.g. with the futurize script)
• to provide Python 3 support for previously Python 2-only libraries with the same APIs as on Python 2 -- particularly with regard to 8-bit strings (the past.builtins.str type).
• to aid in providing minimal-effort Python 3 support for applications using libraries that do not yet wish to upgrade their code properly to Python 3, or wish to upgrade it gradually to Python 3 style.

To install past, use:

$ pip install future

Here are some examples that run identically on Python 3 and 2:

>>> from past.builtins import (str as oldstr, range, reduce,
                               raw_input, xrange)

>>> philosopher = oldstr(u'孔子'.encode('utf-8'))
>>> # This now behaves like a Py2 byte-string on both Py2 and Py3.
>>> # For example, indexing returns a Python 2-like string object, not
>>> # an integer:
>>> philosopher[0]
'å'
>>> type(philosopher[0])


>>> # The div() function behaves like Python 2's / operator
>>> # without "from __future__ import division"
>>> from past.utils import div
>>> div(3, 2)    # like 3/2 in Py2
0
>>> div(3, 2.0)  # like 3/2.0 in Py2
1.5

>>> # List-producing versions of range, reduce, map, filter
>>> from past.builtins import range, reduce
>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])
15

>>> # Other functions removed in Python 3 are resurrected ...
>>> from past.builtins import execfile
>>> execfile('myfile.py')

>>> from past.builtins import raw_input
>>> name = raw_input('What is your name? ')
What is your name? [cursor]

>>> from past.builtins import reload
>>> reload(mymodule)   # equivalent to imp.reload(mymodule) in Python 3

>>> from past.builtins import xrange
>>> for i in xrange(10):
...     pass

It also provides experimental import hooks so you can import and run Python 2 modules from Python 3:

>>> from past import autotranslate
>>> autotranslate('mypy2module')

>>> import mypy2module

Documentation

See .

Credits

Author
Ed Schofield

Sponsor
Python Charmers Pty Ltd, Australia:

Licensing

Copyright 2013-2014 Python Charmers Pty Ltd, Australia. The software is distributed under an MIT licence. See LICENSE.txt.