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Support narrowing unions that include type[None].#16315

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Merged
hauntsaninja merged 7 commits intopython:masterfromtyralla:fix/narrow_nonetype
Jan 14, 2024
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18 changes: 13 additions & 5 deletionsmypy/checker.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -7120,16 +7120,20 @@ def conditional_types_with_intersection(
possible_target_types = []
for tr in type_ranges:
item = get_proper_type(tr.item)
if not isinstance(item, Instance) or tr.is_upper_bound:
return yes_type, no_type
possible_target_types.append(item)
if isinstance(item, (Instance, NoneType)):
possible_target_types.append(item)
if not possible_target_types:
return yes_type, no_type

out = []
errors: list[tuple[str, str]] = []
for v in possible_expr_types:
if not isinstance(v, Instance):
return yes_type, no_type
for t in possible_target_types:
if isinstance(t, NoneType):
errors.append((f'"{v.type.name}" and "NoneType"', '"NoneType" is final'))
continue
intersection = self.intersect_instances((v, t), errors)
if intersection is None:
continue
Expand DownExpand Up@@ -7173,7 +7177,11 @@ def get_isinstance_type(self, expr: Expression) -> list[TypeRange] | None:
elif isinstance(typ, TypeType):
# Type[A] means "any type that is a subtype of A" rather than "precisely type A"
# we indicate this by setting is_upper_bound flag
types.append(TypeRange(typ.item, is_upper_bound=True))
is_upper_bound = True
if isinstance(typ.item, NoneType):
# except for Type[None], because "'NoneType' is not an acceptable base type"
is_upper_bound = False
types.append(TypeRange(typ.item, is_upper_bound=is_upper_bound))
elif isinstance(typ, Instance) and typ.type.fullname == "builtins.type":
object_type = Instance(typ.type.mro[-1], [])
types.append(TypeRange(object_type, is_upper_bound=True))
Expand DownExpand Up@@ -7626,7 +7634,7 @@ def convert_to_typetype(type_map: TypeMap) -> TypeMap:
if isinstance(t, TypeVarType):
t = t.upper_bound
# TODO: should we only allow unions of instances as per PEP 484?
if not isinstance(get_proper_type(t), (UnionType, Instance)):
if not isinstance(get_proper_type(t), (UnionType, Instance, NoneType)):
# unknown type; error was likely reported earlier
return {}
converted_type_map[expr] = TypeType.make_normalized(typ)
Expand Down
19 changes: 12 additions & 7 deletionsmypy/checkexpr.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -385,6 +385,9 @@ def analyze_ref_expr(self, e: RefExpr, lvalue: bool = False) -> Type:
if node.typeddict_type:
# We special-case TypedDict, because they don't define any constructor.
result = self.typeddict_callable(node)
elif node.fullname == "types.NoneType":
# We special case NoneType, because its stub definition is not related to None.
result = TypeType(NoneType())
else:
result = type_object_type(node, self.named_type)
if isinstance(result, CallableType) and isinstance( # type: ignore[misc]
Expand DownExpand Up@@ -511,13 +514,13 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
if is_expr_literal_type(typ):
self.msg.cannot_use_function_with_type(e.callee.name, "Literal", e)
continue
if(
node
and isinstance(node.node, TypeAlias)
and isinstance(get_proper_type(node.node.target), AnyType)
):
self.msg.cannot_use_function_with_type(e.callee.name, "Any", e)
continue
ifnode and isinstance(node.node, TypeAlias):
target = get_proper_type(node.node.target)
if isinstance(target, AnyType):
self.msg.cannot_use_function_with_type(e.callee.name, "Any", e)
continue
if isinstance(target, NoneType):
continue
if (
isinstance(typ, IndexExpr)
and isinstance(typ.analyzed, (TypeApplication, TypeAliasExpr))
Expand DownExpand Up@@ -4733,6 +4736,8 @@ class LongName(Generic[T]): ...
return type_object_type(tuple_fallback(item).type, self.named_type)
elif isinstance(item, TypedDictType):
return self.typeddict_callable_from_context(item)
elif isinstance(item, NoneType):
return TypeType(item, line=item.line, column=item.column)
elif isinstance(item, AnyType):
return AnyType(TypeOfAny.from_another_any, source_any=item)
else:
Expand Down
70 changes: 70 additions & 0 deletionstest-data/unit/check-narrowing.test
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2022,3 +2022,73 @@ def f(x: Union[int, Sequence[int]]) -> None:
):
reveal_type(x) # N: Revealed type is "Tuple[builtins.int, builtins.int]"
[builtins fixtures/len.pyi]

[case testNarrowingIsSubclassNoneType1]
from typing import Type, Union

def f(cls: Type[Union[None, int]]) -> None:
if issubclass(cls, int):
reveal_type(cls) # N: Revealed type is "Type[builtins.int]"
else:
reveal_type(cls) # N: Revealed type is "Type[None]"
[builtins fixtures/isinstance.pyi]

[case testNarrowingIsSubclassNoneType2]
from typing import Type, Union

def f(cls: Type[Union[None, int]]) -> None:
if issubclass(cls, type(None)):
reveal_type(cls) # N: Revealed type is "Type[None]"
else:
reveal_type(cls) # N: Revealed type is "Type[builtins.int]"
[builtins fixtures/isinstance.pyi]

[case testNarrowingIsSubclassNoneType3]
from typing import Type, Union

NoneType_ = type(None)

def f(cls: Type[Union[None, int]]) -> None:
if issubclass(cls, NoneType_):

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One case is still broken, I believe: (python3.10+)

if issubclass(cls, types.Nonetype)

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You are right. The definition in types.pyi is not helpful. I assumed something similar to mentioned test:

NoneType=type(None)

But it is:

@finalclassNoneType:def__bool__(self)->Literal[False]: ...

My suggestion is to letExpressionChecker.analyze_ref_expr directly returnTypeType(NoneType()) when it encounters the full name "types.NoneType". (already pushed)

reveal_type(cls) # N: Revealed type is "Type[None]"
else:
reveal_type(cls) # N: Revealed type is "Type[builtins.int]"
[builtins fixtures/isinstance.pyi]

[case testNarrowingIsSubclassNoneType4]
# flags: --python-version 3.10

from types import NoneType
from typing import Type, Union

def f(cls: Type[Union[None, int]]) -> None:
if issubclass(cls, NoneType):
reveal_type(cls) # N: Revealed type is "Type[None]"
else:
reveal_type(cls) # N: Revealed type is "Type[builtins.int]"
[builtins fixtures/isinstance.pyi]

[case testNarrowingIsInstanceNoIntersectionWithFinalTypeAndNoneType]
# flags: --warn-unreachable --python-version 3.10

from types import NoneType
from typing import final

class X: ...
class Y: ...
@final
class Z: ...

x: X

if isinstance(x, (Y, Z)):
reveal_type(x) # N: Revealed type is "__main__.<subclass of "X" and "Y">"
if isinstance(x, (Y, NoneType)):
reveal_type(x) # N: Revealed type is "__main__.<subclass of "X" and "Y">1"
if isinstance(x, (Y, Z, NoneType)):
reveal_type(x) # N: Revealed type is "__main__.<subclass of "X" and "Y">2"
if isinstance(x, (Z, NoneType)): # E: Subclass of "X" and "Z" cannot exist: "Z" is final \
# E: Subclass of "X" and "NoneType" cannot exist: "NoneType" is final
reveal_type(x) # E: Statement is unreachable

[builtins fixtures/isinstance.pyi]
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