Stuart, thanks for clearly laying out the issue and coming up with a patch.
So, there's the "old style" cleandoc output generated by Python 3.12, a "new style" output for the same function in 3.13 (stripping more whitespace), and the patch then introduces a third option that produces the same output under both 3.12 and 3.13 but doesn't match the "native" output of either one. Short term, adding the patch eliminates the issue introduced by the changes to the docstring handling in 3.13. Unfortunately, it also seems to require keeping the patch around after the transition from 3.12 to 3.13 is complete, even though the problem is tied to the transition between these specific versions. Given that trixie is to ship with 3.13 as the sole supported Python version (and work on that seems to be progressing nicely), once 3.12 gets dropped and all Python packages rebuilt for 3.13-only, the performance issues would be history even if no action were taken on the ply end. Looking at the cleandoc functions in inspect.py [1] and compile.c [2], the only documented difference between them seems to be the latter not removing leading and trailing empty lines. Is there any reason the _normalize function in your patch couldn't mimick 3.13's inspect.cleandoc [1], minus the removal of empty lines, to produce output compatible with 3.13's compile.c under both 3.12 and 3.13? That way, once 3.12 is dropped from the supported Python version in Debian, the patch in ply could be dropped as well. [1]https://github.com/python/cpython/blob/b93b7e566e5a4efe7f077af2083140e50bd2b08f/Lib/inspect.py#L788 [2]https://github.com/python/cpython/blob/8cd7f8bf8d6b62f30a8bba1f968eb0c593a8781a/Python/compile.c#L1408
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