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Merged
merged 5 commits into from
Dec 11, 2024
Merged

Do not allow type[] to contain Literal types #18276

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7c31a94
Do not allow `type[]` to contain `Literal` types
sobolevn Dec 10, 2024
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Fix CI
sobolevn Dec 10, 2024
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6 changes: 3 additions & 3 deletions mypy/typeanal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -652,14 +652,14 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
# To prevent assignment of 'builtins.type' inferred as 'builtins.object'
# See https://github.com/python/mypy/issues/9476 for more information
return None
type_str = "Type[...]" if fullname == "typing.Type" else "type[...]"
if len(t.args) != 1:
type_str = "Type[...]" if fullname == "typing.Type" else "type[...]"
self.fail(
type_str + " must have exactly one type argument", t, code=codes.VALID_TYPE
f"{type_str} must have exactly one type argument", t, code=codes.VALID_TYPE
)
item = self.anal_type(t.args[0])
if is_bad_type_type_item(item):
self.fail("Type[...] can't contain another Type[...]", t, code=codes.VALID_TYPE)
self.fail(f'{type_str} can\'t contain "{item}"', t, code=codes.VALID_TYPE)
item = AnyType(TypeOfAny.from_error)
return TypeType.make_normalized(item, line=t.line, column=t.column)
elif fullname == "typing.ClassVar":
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9 changes: 5 additions & 4 deletions mypy/types_utils.py
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Expand Up @@ -15,6 +15,7 @@
AnyType,
CallableType,
Instance,
LiteralType,
NoneType,
Overloaded,
ParamSpecType,
Expand Down Expand Up @@ -81,14 +82,14 @@ def is_bad_type_type_item(item: Type) -> bool:
Such types are explicitly prohibited by PEP 484. Also, they cause problems
with recursive types like T = Type[T], because internal representation of
TypeType item is normalized (i.e. always a proper type).

Also forbids `Type[Literal[...]]`, because typing spec does not allow it.
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@JelleZijlstra JelleZijlstra Dec 10, 2024

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I think it might be better to frame this in terms of what is allowed. Here are some other things mypy allows that I don't think make sense: https://mypy-play.net/?mypy=latest&python=3.12&gist=aa900cb6c86fd55901b21ee182aa35ec

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@sobolevn sobolevn Dec 10, 2024 •
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I suspected that this will be brought up :)
I would prefer to keep this PR focused on just one thing. Because, for example, I only agree with the first example: type[TypeGuard[int]], but it is a completely different thing to fix.

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@sobolevn sobolevn Dec 10, 2024

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I think that we can clarify this in https://github.com/python/typing/tree/main/docs/spec

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@JelleZijlstra JelleZijlstra Dec 10, 2024

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This is already specified in the grammar at https://typing.readthedocs.io/en/latest/spec/annotations.html#type-and-annotation-expressions . (Though I noticed we're missing unions there, which should be supported.)

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@JelleZijlstra JelleZijlstra Dec 10, 2024

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I'm fine with deferring other similar changes to other PRs, though.

"""
item = get_proper_type(item)
if isinstance(item, TypeType):
if isinstance(item, (TypeType, LiteralType)):
return True
if isinstance(item, UnionType):
return any(
isinstance(get_proper_type(i), TypeType) for i in flatten_nested_unions(item.items)
)
return any(is_bad_type_type_item(typ) for typ in flatten_nested_unions(item.items))
return False


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9 changes: 9 additions & 0 deletions test-data/unit/check-literal.test
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Expand Up @@ -2984,3 +2984,12 @@ class C(Base):
reveal_type(sep) # N: Revealed type is "Union[Literal['a'], Literal['b']]"
return super().feed_data(sep)
[builtins fixtures/tuple.pyi]

[case testLiteralInsideAType]
from typing_extensions import Literal
from typing import Type, Union

x: Type[Literal[1]] # E: Type[...] can't contain "Literal[1]"
y: Type[Union[Literal[1], Literal[2]]] # E: Type[...] can't contain "Union[Literal[1], Literal[2]]"
z: Type[Literal[1, 2]] # E: Type[...] can't contain "Union[Literal[1], Literal[2]]"
[builtins fixtures/tuple.pyi]
6 changes: 4 additions & 2 deletions test-data/unit/check-recursive-types.test
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Expand Up @@ -409,8 +409,10 @@ def local() -> None:
x: L
reveal_type(x) # N: Revealed type is "builtins.list[Union[builtins.int, Any]]"

S = Type[S] # E: Type[...] can't contain another Type[...]
U = Type[Union[int, U]] # E: Type[...] can't contain another Type[...]
S = Type[S] # E: Type[...] can't contain "type[<placeholder __main__.S>]" \
# E: Type[...] can't contain "type[Any]"
U = Type[Union[int, U]] # E: Type[...] can't contain "Union[builtins.int, Union[type[builtins.int], type[<placeholder __main__.U>]]]" \
# E: Type[...] can't contain "Union[builtins.int, type[Any]]"
x: U
reveal_type(x) # N: Revealed type is "Type[Any]"

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