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Correctly narrow types for tuple[type[X], ...] #15691

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Jul 29, 2023
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Correctly narrow types for tuple[type[X], ...] #15691

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897c12b
Correctly narrow types for `tuple[type[X], ...]`
sobolevn Jul 16, 2023
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sobolevn Jul 16, 2023
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sobolevn Jul 29, 2023
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2 changes: 2 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7118,6 +7118,8 @@ def flatten_types(t: Type) -> list[Type]:
t = get_proper_type(t)
if isinstance(t, TupleType):
return [b for a in t.items for b in flatten_types(a)]
elif is_named_instance(t, "builtins.tuple"):
return [t.args[0]]
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Why is it correct to use all args in former case but just first arg in second case?

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Because tuple has only one arg. FWIW the only real question here is whether we need to recurse, i.e. also support:

  • tuple[tuple[type[A], type[B]], ...]
  • tuple[tuple[type[A], ...], ...]

But TBH I don't really care, because it would be a corner case to already rare special case.

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I've decided not to, because this can be quite complex / slow with no real users asking for it.

else:
return [t]

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47 changes: 47 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -1268,3 +1268,50 @@ def g() -> None:
def foo(): ...
foo()
[builtins fixtures/dict.pyi]


[case testNarrowingWithTupleOfTypes]
from typing import Tuple, Type

class Base: ...

class Impl1(Base): ...
class Impl2(Base): ...

impls: Tuple[Type[Base], ...] = (Impl1, Impl2)
some: object

if isinstance(some, impls):
reveal_type(some) # N: Revealed type is "__main__.Base"
else:
reveal_type(some) # N: Revealed type is "builtins.object"

raw: Tuple[type, ...]
if isinstance(some, raw):
reveal_type(some) # N: Revealed type is "builtins.object"
else:
reveal_type(some) # N: Revealed type is "builtins.object"
[builtins fixtures/dict.pyi]


[case testNarrowingWithTupleOfTypesPy30Plus]
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# flags: --python-version 3.10
class Base: ...

class Impl1(Base): ...
class Impl2(Base): ...

impls: tuple[type[Base], ...] = (Impl1, Impl2)
some: int | Base
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if isinstance(some, impls):
reveal_type(some) # N: Revealed type is "__main__.Base"
else:
reveal_type(some) # N: Revealed type is "Union[builtins.int, __main__.Base]"

raw: tuple[type, ...]
if isinstance(some, raw):
reveal_type(some) # N: Revealed type is "Union[builtins.int, __main__.Base]"
else:
reveal_type(some) # N: Revealed type is "Union[builtins.int, __main__.Base]"
[builtins fixtures/dict.pyi]