[ty] Add precise iteration and unpacking inference for string literals and bytes literals #20023
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Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
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Okay, this one's pretty cool -- ty is now able to infer that all possibilities have been exhaustively covered here, meaning the variable cannot possibly be undefined by the time the code reaches the assertion at the bottom: https://github.com/scipy/scipy/blob/99c0ef6af161a4d8157cae5276a20c30b7677c6f/scipy/linalg/tests/test_lapack.py#L147-L171 |
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This is a good example of the sort of issue that led us to disable |
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…s and bytes literals (astral-sh#20023) ## Summary Previously we held off from doing this because we weren't sure that it was worth the added complexity cost. But our code has changed in the months since we made that initial decision, and I think the structure of the code is such that it no longer really leads to much added complexity to add precise inference when unpacking a string literal or a bytes literal. The improved inference we gain from this has real benefits to users (see the mypy_primer report), and this PR doesn't appear to have a performance impact. ## Test plan mdtests
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Summary
Previously we held off from doing this because we weren't sure that it was worth the added complexity cost. But our code has changed in the months since we made that initial decision, and I think the structure of the code is such that it no longer really leads to much added complexity to add precise inference when unpacking a string literal or a bytes literal.
The improved inference we gain from this has real benefits to users (see the mypy_primer report), and this PR doesn't appear to have a performance impact.
Test plan
mdtests