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Spurious error with partial and ParamSpec #15215
Description
Bug Report
When type checking the code below mypy produces a bunch of weird errors, most interesting one being
Argument 1 to "partial" has incompatible type "Callable[[Callable[_P, _T], NamedArg(str, 'name')], Task[_P, _T]]"; expected "Callable[..., Task[_P, _T]]" [arg-type]
I'm not sure, but isn't Callable[[Something], Task[_P, _T]] always compatible with Callable[..., Task[_P, _T]]?
To Reproduce
You can also see this in playground.
from __future__ import annotations
from dataclasses import dataclass
from functools import partial
from typing import Any, TypeVar, ParamSpec, Generic, Protocol, Callable
_T = TypeVar("_T")
_P = ParamSpec("_P")
@dataclass(kw_only=True, repr=True)
class Task(Generic[_P, _T]):
name: str
function: Callable[_P, _T]
class _TaskRegistrator(Protocol):
def __call__(self, func: Callable[_P, _T], /, *, name: str = ...) -> Task[_P, _T]:
...
class TaskQueue:
def _register_task(self, func: Callable[_P, _T], *, name: str) -> Task[_P, _T]:
# Actual implementation omitted
return Task(name=name, function=func)
def task(self, name: str) -> _TaskRegistrator:
return partial(self._register_task, name=name) # E: see below (L29)
def task2(self, name: str) -> Callable[[Callable[_P, _T]], Task[_P, _T]]:
return partial(self._register_task, name=name) # E: see below (L32)
# And now we see that the problem is even unrelated to `self`:
def _register_task(func: Callable[_P, _T], *, name: str) -> Task[_P, _T]:
# Actual implementation omitted
return Task(name=name, function=func)
def task(name: str) -> _TaskRegistrator:
return partial(_register_task, name=name) # E: see below (L42)Expected Behavior
From my understanding, no mypy errors should be pointed out. pyright agrees with me (just to test on another typechecker) - all green - but I'm not ready to switch from convenient mypy to pyright (I personally dislike that project for being non-python in python ecosystem, plus my current project relies heavily on Django plugin).
Actual Behavior
Several errors, all located on lines with partial(...) calls.
main.py:29: error: Argument 1 to "partial" has incompatible type "Callable[[Callable[_P, _T], NamedArg(str, 'name')], Task[_P, _T]]"; expected "Callable[..., Task[_P, _T]]" [arg-type]
main.py:32: error: Incompatible return value type (got "partial[Task[_P, _T]]", expected "Callable[[Callable[_P, _T]], Task[_P, _T]]") [return-value]
main.py:32: note: "partial[Task[_P, _T]].__call__" has type "Callable[[VarArg(Any), KwArg(Any)], Task[_P, _T]]"
main.py:32: error: Argument 1 to "partial" has incompatible type "Callable[[Callable[_P, _T], NamedArg(str, 'name')], Task[_P, _T]]"; expected "Callable[..., Task[_P, _T]]" [arg-type]
main.py:42: error: Argument 1 to "partial" has incompatible type "Callable[[Callable[_P, _T], NamedArg(str, 'name')], Task[_P, _T]]"; expected "Callable[..., Task[_P, _T]]" [arg-type]
Found 4 errors in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.2.0, then master and all versions since 0.990.
- Mypy command-line flags: none (with and without
--strictresult is the same) - Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.10
Activity
Erase stray typevars in functools.partial generic (python#18954)