mypy incorrectly tags function argument TypeVar with return type when called from a caller with the same signature #16924
Description
Bug Report
mypy incorrectly tags a function argument of type Mapping[K, V] where K and V are TypeVar with the return value of the caller function.
To Reproduce
The below small program demonstrates the issue:
from typing import Dict, Mapping, TypeVar, Union
K = TypeVar("K")
V = TypeVar("V")
K2 = TypeVar("K2")
V2 = TypeVar("V2")
def func(one: Dict[K, V], two: Mapping[K2, V2]) -> Dict[Union[K, K2], Union[V, V2]]:
reveal_type(one)
reveal_type(two)
return {}
def caller(arg1: Mapping[K, V], arg2: Mapping[K2, V2]) -> Dict[Union[K, K2], Union[V, V2]]:
reveal_type(arg1)
reveal_type(arg2)
_arg1 = arg1 if isinstance(arg1, dict) else dict(arg1)
return func(_arg1, arg2)Expected Behavior
mypy should succeed without an error.
$ mypy --strict break_mypy.py
break_mypy.py:10: note: Revealed type is "builtins.dict[K`-1, V`-2]"
break_mypy.py:11: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
break_mypy.py:16: note: Revealed type is "typing.Mapping[K`-1, V`-2]"
break_mypy.py:17: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
Success: no issues found in 1 source file
Actual Behavior
mypy complains with a very weird error, even though the revealed types are correct
$ mypy --strict break_mypy.py
break_mypy.py:10: note: Revealed type is "builtins.dict[K`-1, V`-2]"
break_mypy.py:11: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
break_mypy.py:16: note: Revealed type is "typing.Mapping[K`-1, V`-2]"
break_mypy.py:17: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
break_mypy.py:19: error: Argument 2 to "func" has incompatible type "Mapping[K2, V2]"; expected "Mapping[Union[K, K2], Union[V, V2]]" [arg-type]
Found 1 error in 1 file (checked 1 source file)
More Info
Note, if I change the type signature of the caller, it ends up changing the type signature of the called function as well:
from typing import Dict, Mapping, TypeVar, Union
K = TypeVar("K")
V = TypeVar("V")
K2 = TypeVar("K2")
V2 = TypeVar("V2")
def func(one: Dict[K, V], two: Mapping[K2, V2]) -> Dict[Union[K, K2], Union[V, V2]]:
reveal_type(one)
reveal_type(two)
return {}
def caller(arg1: Mapping[K, V], arg2: Mapping[K2, V2]) -> None:
reveal_type(arg1)
reveal_type(arg2)
_arg1 = arg1 if isinstance(arg1, dict) else dict(arg1)
func(_arg1, arg2)will return:
$ mypy --strict break_mypy.py
break_mypy.py:10: note: Revealed type is "builtins.dict[K`-1, V`-2]"
break_mypy.py:11: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
break_mypy.py:16: note: Revealed type is "typing.Mapping[K`-1, V`-2]"
break_mypy.py:17: note: Revealed type is "typing.Mapping[K2`-3, V2`-4]"
Success: no issues found in 1 source file
Your Environment
- Mypy version used:
mypy 0.991 (compiled: yes) - Mypy command-line flags:
--strict - Mypy configuration options from
mypy.ini(and other config files):ignore_missing_imports = true - Mypy plugins:
sqlalchemy.ext.mypy.plugin,pydantic.mypyandnumpy.typing.mypy_plugin - Python version used:
Python 3.9.17