feat: constant fold common builtin call expressions [3/3] - #19886
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BobTheBuidler
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| y = x # E: Cannot determine type of "x" # E: Name "x" is used before definition | ||
| y() | ||
| y = x # E: Name "x" is used before definition | ||
| y() # E: "int" not callable |
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I think this might indicate a bug in mypy itself? I don't think this should change just from the constant folding
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October 1, 2025 23:23
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One example of where this would be useful: mypyc/mypyc#1152 |
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Currently, `translate_len` can determine the length of an RTuple at compile time This PR extends this capability to all expressions supported by `get_expr_length_value` This will constant fold the code example displayed in mypyc/mypyc#1152 without waiting for the implementation of #19886 which has a few steps ahead of it Before: ```python def extend_and_specialize(items: list[dict[str, Any]]) -> None: types: Final[dict[str, Any]] = {i["name"]: i for i in items} types.update( { k[len("https://w3id.org/cwl/salad#") :]: v for k, v in types.items() if k.startswith("https://w3id.org/cwl/salad#") } ) ``` After: ```python def extend_and_specialize(items: list[dict[str, Any]]) -> None: types: Final[dict[str, Any]] = {i["name"]: i for i in items} types.update( { k[27 : ]: v for k, v in types.items() if k.startswith("https://w3id.org/cwl/salad#") } ) ``` Even after #19986, this will also work for some situations that constant folding cannot handle but `get_expr_length` can.
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This PR implements constant folding for builtin callables where possible.
If all args are constant foldable and the callable is one of the builtin callables below, mypy can, in most cases, fold the result.
The supported builtins are:
While this PR does not build off of #19885, it does need to come afterward because it contains a refactoring that moves around the code introduced in 19885.