Allow unpacking from TypeVars with iterable bounds #13425
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TypeVars aren't iterable, but their bounds might be! Resolve a TypeVar to its bounds before trying to decide how to unpack one of its instances. Fixes python#13402.
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sobolevn reviewed Aug 17, 2022
| from typing import Tuple, TypeVar | ||
| TupleT = TypeVar("TupleT", bound=Tuple[int, ...]) | ||
| def f(t: TupleT) -> None: | ||
| a, *b = t |
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Let's add reveal_type(a) and reveal_type(b) here. This would catch some unexpected types.
sobolevn reviewed Aug 17, 2022
| rvalue_type = get_proper_type(rv_type or self.expr_checker.accept(rvalue)) | ||
| | ||
| if isinstance(rvalue_type, TypeVarType): | ||
| rvalue_type = get_proper_type(rvalue_type.upper_bound) |
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What if there's no upper bound? 🤔 Let's add a test case for this as well!
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That's a good thing to check 😅 It looks like it does the right thing!
I left the first test case in check-bound.test and added the new test case to check-typevar-unbound.test but let me know if they should be organized differently.
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| Thanks for your help! |
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| According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉 |
hauntsaninja pushed a commit to hauntsaninja/mypy that referenced this pull request Sep 10, 2022
* Allow unpacking from TypeVars by resolving bounds TypeVars aren't iterable, but their bounds might be! Resolve a TypeVar to its bounds before trying to decide how to unpack one of its instances. Fixes python#13402.
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Description
TypeVars aren't iterable, but their bounds might be! Resolve a TypeVar to its bounds before trying to decide how to unpack one of its instances. This allows unpacking from instances of TypeVars with iterable bounds, which otherwise fails.
Fixes #13402.
Test Plan
Added a test for a minimal reproducer.