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.. _backwards-conversion:
``pasteurize``: Py3 to Py2/3
----------------------------
Running ``pasteurize -w mypy3module.py`` turns this Python 3 code::
import configparser
import copyreg
class Blah:
pass
print('Hello', end=None)
into this code which runs on both Py2 and Py3::
from __future__ import print_function
from future import standard_library
standard_library.install_hooks()
import configparser
import copyreg
class Blah(object):
pass
print('Hello', end=None)
Notice that both ``futurize`` and ``pasteurize`` create explicit new-style
classes that inherit from ``object`` on both Python versions, and both
refer to stdlib modules (as well as builtins) under their Py3 names.
Note also that the ``configparser`` module is a special case; there is a full
backport available on PyPI (https://pypi.org/project/configparser/), so, as
of v0.16.0, ``python-future`` no longer provides a ``configparser`` package
alias. To use the resulting code on Py2, install the ``configparser`` backport
with ``pip install configparser`` or by adding it to your ``requirements.txt``
file.
``pasteurize`` also handles the following Python 3 features:
- keyword-only arguments
- metaclasses (using :func:`~future.utils.with_metaclass`)
- extended tuple unpacking (PEP 3132)
To handle function annotations (PEP 3107), see :ref:`func_annotations`.
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