PEP 686: Make UTF-8 mode default

[vstinner (Victor Stinner)]

@malemburg

For the general public and there esp. for the Windows users, there needs to be more time to raise awareness and have users adapt, though, since the change can cause silent data corruption.

What will be done to raise awareness? My fear is that if nobody is being done, the situation will be identical in 2026 than in 2022: nobody will fix any issue in the meanwhile.

@malemburg

We first have to tell people that the change is coming, point them to the UTF-8 mode to test their installations and give them time to make any necessary changes.

How do you plan to tell people?

@malemburg

By reminding people of the upcoming major change for a few releases we make sure that everyone is aware and can plan for the change. This is esp. important for larger companies with millions of LOC written in Python.

My colleague Tomáš Hrnčiar rebuilt all Python packages in Fedora with PYTHONWARNDEFAULTENCODING enabled. On 3891 packages, 143 packages (4%) failed to build: Please try PYTHONWARNDEFAULTENCODING (PEP 597) - #5 by hrnciar

Do we need to wait until this number (143) or this ratio (4%) is moving below a limit? For example, is it ok if only 50 fail to build? Or 10?

We don’t have access to private code written behind closed door, but we can use public code to estimate how private code will be affected. Also, we can make sure that most important packages on PyPI are ready for these changes. For example, are top 50 PyPI packages ready for PEP 686? What about top 100, or top 5000?

If there are important milestone and actions must be done, wan we put such migration path as part of PEP 686?