fix: Make stringified expressions valid and faithful Python#478
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gaoflow wants to merge 2 commits into
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fix: Make stringified expressions valid and faithful Python#478gaoflow wants to merge 2 commits into
gaoflow wants to merge 2 commits into
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Fixes several classes of invalid or unfaithful output from str(expr),
found with a systematic round-trip audit of expression rendering
(parse -> Expr -> str -> re-parse must succeed and be AST-equivalent):
- Lambda parameter sections: the keyword-only marker was emitted even
after *args (lambda *a, *, z=2: z), section markers were emitted after
* and ** (lambda x, */, a: a), and the / marker was dropped when all
parameters are positional-only (lambda x, /: x rendered lambda x: x).
- F-string conversions and format specifiers were dropped entirely:
f'{x!r:>10}' rendered as f'{x}'. Same for t-string interpolations on
Python 3.14, which also lost the quotes of string constants.
- Missing required parentheses: generator expressions in grouping
contexts ({1: g for g in y} re-parses as a dict comprehension), walrus
assignments in dict keys/values, slice bounds and comprehension
conditions, integer-literal attribute access (1.bit_length()), and
lambdas/walrus in f-string replacement fields where the colon would
start the format specifier.
- The subscript_slice context flag leaked into slice bounds, marking
tuples implicit: o[(a, b):y] rendered as o[a, b:y].
- Spurious parentheses from iterate() call sites relying on the ATOMIC
default: f(a=(b + c)), o[(a + b):], [(x + 1) for x in y], etc.
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Thanks for your contribution. Again, please follow our PR template. |
pawamoy
reviewed
Jul 16, 2026
Contributor
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Updated the PR body to follow the template, including the AI-use checkbox. I also pushed f79da51 for the review suggestions. |
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Description of the change
str(Expr)could emit invalid or semantically different Python for lambda parameter markers, formatted strings, generator expressions, integer-literal attributes, slices, and precedence-sensitive contexts.This fixes the shared rendering and building paths and adds a parse → Expr → str → parse matrix that checks AST equivalence across expression shapes and contexts. The full griffelib suite passes on Python 3.12; the focused expression and node suites pass on Python 3.10 and 3.14.
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