mypy
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Published
20 hours ago •
python
python
Function return type TypeVar is assumed to be base class for TypeVar bound to UnionType
Bug Report
A function defined as
def assert_not_none(x: Optional[T]) -> T:
assert x is not None
return x
used with an input Optional[Union[A, B]] should return a type Union[A, B], but mypy 1.3.0 currently assumes that it returns the base class of A and B (or builtins.object if there is no other common base). (Note: pylance correctly identifies the return type as Union[A, B].)
To Reproduce
run mypy on the following file.
from typing import Literal, Optional, TypeVar, Union
from pydantic import BaseModel
T = TypeVar("T")
def assert_not_none(x: Optional[T]) -> T:
assert x is not None
return x
class Foo(BaseModel):
foo: Literal[True]
class Bar(BaseModel):
bar: Literal[True]
FooOrBar = Union[Foo, Bar]
def validate(input: Optional[FooOrBar]):
reveal_type(input) # as expected: Union[Foo, Bar, None]
reveal_type(assert_not_none(input)) # expected: Union[Foo, Bar], actual: pydantic.main.BaseModel
assert input is not None
reveal_type(input) # as expected: Union[Foo, Bar]
Expected Behavior
reveal_type(assert_not_none(input)) should be Union[Foo, Bar]
Actual Behavior
reveal_type(assert_not_none(input)) actually is pydantic.main.BaseModel.
Your Environment
- Mypy version used: 1.3.0 (compiled: yes)
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.8.10
