[3.14] gh-143054: Disallow non-top-level Cut for now (GH-143622)#143790
Merged
encukou merged 1 commit intopython:3.14from Jan 15, 2026
Merged
[3.14] gh-143054: Disallow non-top-level Cut for now (GH-143622)#143790encukou merged 1 commit intopython:3.14from
encukou merged 1 commit intopython:3.14from
Conversation
The behaviour of Cut in nested parentheses, Repeat, Opt, and similar is somewhat chaotic. Apparently even the academic papers on PEG aren't as clear as they could be. And it doesn't really matter. Python only uses top-level cuts. When that changes, we can clarify as much as necessary (and even change the implementation to make sense for what we'll need). Document that this is deliberately unspecified, and add a test to make sure any decision is deliberate, tested and documented. (cherry picked from commit f0a0467) Co-authored-by: Petr Viktorin <encukou@gmail.com>
miss-islington
requested review from
AA-Turner,
lysnikolaou,
pablogsal and
willingc
as code owners
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
The behaviour of Cut in nested parentheses, Repeat, Opt, and similar
is somewhat chaotic. Apparently even the academic papers on PEG aren't
as clear as they could be.
And it doesn't really matter. Python only uses top-level cuts.
When that changes, we can clarify as much as necessary (and even
change the implementation to make sense for what we'll need).
Document that this is deliberately unspecified, and add a test to
make sure any decision is deliberate, tested and documented.
(cherry picked from commit f0a0467)
Co-authored-by: Petr Viktorin encukou@gmail.com
📚 Documentation preview 📚: https://cpython-previews--143790.org.readthedocs.build/