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Refactor: simplify combine_function_signatures by reducing line count and preserving comments #19196

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This pull request contributes to issue #5917, which encourages the decomposition and simplification of overly long methods to improve code clarity and maintainability.

Summary of changes

Refactored the combine_function_signatures method to reduce line count and eliminate redundancy, while preserving all original logic and explanatory comments.

Key improvements:

  • Reduced vertical space and simplified control flow
  • Preserved all original comments, including the TODO
  • Kept behavior unchanged and all test cases passing

Notes

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new_returns: list[Type] = []

new_args: list[list[Type]] = [[] for _ in callables[0].arg_types]
new_kinds, new_returns = list(callables[0].arg_kinds), []
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@sterliakov sterliakov Jun 1, 2025

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This looks like a penalty to readability rather than refactoring, why merge two unrelated assignments?

@@ -3160,18 +3160,16 @@ def combine_function_signatures(self, types: list[ProperType]) -> AnyType | Call
if len(new_kinds) != len(target.arg_kinds):
too_complex = True
break
for i, (new_kind, target_kind) in enumerate(zip(new_kinds, target.arg_kinds)):
if new_kind == target_kind:
for i, (k1, k2) in enumerate(zip(new_kinds, target.arg_kinds)):
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I think new_ and target_ prefixes are much clearer than k1 and k2...

return callables[0].copy_modified(
arg_types=final_args,
arg_types=[make_simplified_union(args) for args in new_args],
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This is definitely an improvement!

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github-actions bot commented Jun 1, 2025

Diff from mypy_primer, showing the effect of this PR on open source code:

nox (https://github.com/wntrblm/nox): 1.31x slower (30.9s -> 40.5s in single noisy sample)

typeshed-stats (https://github.com/AlexWaygood/typeshed-stats): 1.55x slower (66.3s -> 102.5s in single noisy sample)

materialize (https://github.com/MaterializeInc/materialize): 1.06x slower (135.9s -> 144.5s in single noisy sample)

imagehash (https://github.com/JohannesBuchner/imagehash): 1.06x slower (74.0s -> 78.8s in single noisy sample)

discord.py (https://github.com/Rapptz/discord.py): 1.10x slower (281.1s -> 308.0s in single noisy sample)

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2 participants