[Experimental] Run Python 2 code from 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 'å' >>> type(philosopher) <past.builtins.oldstr> >>> # 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
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