This page is primarily intended for developers of Mercurial.

Python 3

This is a status page for keeping track of what needs to be done to make progress on Mercurial on Python 3.

1. Status

Mercurial 5.2 is the first release that officially has support for Python 3. Supported Python 3 versions are 3.5, 3.6, 3.7, and 3.8. Mercurial with Python 3 on Windows is tested regularly, but there remains some known issues outside of the core.

It is the project policy for Mercurial and its core extensions to be compatible with Python 3. Over 99% of tests pass with Python 3 and test regressions are treated seriously.

Most used 3rd party extensions like evolve and topic have been ported to Python 3. There are some which have not yet been ported.

We will drop support for Python 2.7 for the Mercurial 6.1 release.

2. Using

Since Mercurial 5.2, no longer refuses to run with Python 3. pip install Mercurial or python install should work out of the box. But be aware that Windows support is still considered a beta level.

No run-time environment variable or config option is required to use Python 3 with Mercurial: only the installation step / requires special action to override the Python version check.

3. Things need to be investigated

4. Porting Extensions to Python 3

Nearly every extension will need to be ported to be compatible with Python 3. This is because of fundamental differences between Python 2 and Python 3.

The source code for Mercurial extensions will need to be Python 3 native and will need to be compatible with Mercurial's APIs. In many cases, existing source code will compile on Python 3 but will fail at run-time. Sources of run-time errors include:

Do an Internet search for Python 3 porting to find well-written and comprehensive guides on generically porting code to Python 3.

Extension authors may find the mercurial.pycompat module useful. This modules contains abstractions and utilities for bridging the differences between Python 2 and 3. It is conceptually similar to the six Python module.

If you need help or guidance on porting extensions, you can message on IRC or the development MailingList. We will be happy to help you.


Python3 (last edited 2021-11-09 22:31:50 by RaphaelGomes)