PEP 765: specify when the SyntaxWarning will be emitted, and explain why

[iritkatriel]

• Change is either:
  • To a Draft PEP
  • To an Accepted or Final PEP, with Steering Council approval
  • To fix an editorial issue (markup, typo, link, header, etc)
• PR title prefixed with PEP number (e.g. PEP 123: Summary of changes)

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[konstin]

This does not need to be solve here, but it's relevant to this change: In uv, we found that the current behavior of emitting syntax warnings is confusing to users, with the defaults from pip they don't see the syntax warnings. astral-sh/uv#1928 (comment)

[hauntsaninja]

Yes, uv's current default behaviour is to skip precompilation at installation time. If a uv user uses --compile-bytecode they will not see a warning (most users should use that flag! especially if uv implements astral-sh/uv#2637 to match pip's performance)

[ncoghlan]

LGTM!