[Python-Dev] PEP 4000 to explicitly declare we won't be doing a Py3k style compatibility break again?

Nick Coghlan ncoghlan at gmail.com
Sun Aug 17 03:28:48 CEST 2014

I've seen a few people on python-ideas express the assumption that
there will be another Py3k style compatibility break for Python 4.0.

I've also had people express the concern that "you broke compatibility
in a major way once, how do we know you won't do it again?".

Both of those contrast strongly with Guido's stated position that he
never wants to go through a transition like the 2->3 one again.

Barry wrote PEP 404 to make it completely explicit that python-dev had
no plans to create a Python 2.8 release. Would it be worth writing a
similarly explicit "not an option" PEP explaining that the regular
deprecation and removal process (roughly documented in PEP 387) is the
*only* deprecation and removal process? It could also point to the
fact that we now have PEP 411 (provisional APIs) to help reduce our
chances of being locked indefinitely into design decisions we aren't
happy with.

If folks (most signficantly, Guido) are amenable to the idea, it
shouldn't take long to put such a PEP together, and I think it could
help reduce some of the confusions around the expectations for Python
4.0 and the evolution of 3.x in general.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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