Purpose of the project

Modernize is a Python program that reads Python 2 source code and applies a series of fixers to transform it into source code that is valid on both Python 3 and Python 2.7.

This allows you to run your test suite on Python 2.7 and Python 3 so you can gradually port your code to being fully Python 3 compatible without slowing down development of your Python 2 project.

The python -m modernize command works like python -m fissix, see fissix. Here’s how you’d rewrite a single file:

python -m modernize -w

It does not guarantee, but it attempts to spit out a codebase compatible with Python 2.6+ or Python 3. The code that it generates has a runtime dependency on six, unless the --no-six option is used. Version 1.9.0 or later of six is recommended. Some of the fixers output code that is not compatible with Python 2.5 or lower.

Once your project is ready to run in production on Python 3 it’s recommended to drop Python 2.7 support using pyupgrade

See the LICENSE file for the license of modernize. Using this tool does not affect licensing of the modernized code.

This library is a very thin wrapper around fissix, a fork of lib2to3.

The project website can be found on GitHub and the PyPI project name is modernize

A note about handling text literals

  • By default modernize does not change Unicode literals at all, which means that you can take advantage of PEP 414. This is the simplest option if you only want to support Python 3.3 and above along with Python 2.

  • Alternatively, there is the --six-unicode flag which will wrap Unicode literals with the six helper function six.u() using the modernize.fixes.fix_unicode fixer. This is useful if you want to support Python 3.1 and Python 3.2 without bigger changes.

  • The last alternative is the --future-unicode flag which imports the unicode_literals from the __future__ module using the modernize.fixes.fix_unicode_future fixer. This requires Python 2.6 and later, and will require that you mark bytestrings with b'' and native strings in str('') or something similar that survives the transformation.

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