Mypy 1.11.0 complains about Task typing

[williamjamir]

Bug summary

Something has changed from mypy 1.10.1 to 1.11.0 that altered the behavior related to Task typing.
Consider this snippet:

from functools import partial
from typing import reveal_type

from prefect import task


@task
def test(a: int, b: int) -> None: ...


partial(test, a=1)
reveal_type(test)

I got the following output on mypy 1.11.0

 mypy acme.py
acme.py:10: error: "Task[[int, int], None]" not callable  [misc]
acme.py:11: note: Revealed type is "prefect.tasks.Task[[a: builtins.int, b: builtins.int], None]"

But I got the following output on mypy 1.10.1

 mypy acme.py           
acme.py:11: note: Revealed type is "prefect.tasks.Task[[a: builtins.int, b: builtins.int], None]"
Success: no issues found in 1 source file

Version info (prefect version output)

Version:             2.16.9
API version:         0.8.4
Python version:      3.11.5
Git commit:          083def52
Built:               Thu, Apr 4, 2024 3:11 PM
OS/Arch:             darwin/arm64
Profile:             default
Server type:         server

Additional context

No response

[zzstoatzz]

thanks @williamjamir for the issue! will take a look at this

[zzstoatzz]

hi @williamjamir

using this MRE

» cat repros/task_typing.py
from functools import partial
from typing import reveal_type

from prefect import task

@task
def test(a: int, b: int) -> None: ...

partial(test, a=1)
reveal_type(test)

and this version of mypy

» pip freeze | rg mypy
mypy==1.11.0
mypy-extensions==1.0.0

I am not yet able to reproduce this on 2.16.9, newest 2.x, or 3.x

specific version checks

## 2.16.9
» uv pip install prefect==2.16.9 --force-reinstall
...
» mypy repros/task_typing.py
repros/task_typing.py:12: note: Revealed type is "Any"
Success: no issues found in 1 source file

## newest 2.x
» uv pip install -U prefect
...
» mypy repros/task_typing.py
repros/task_typing.py:12: note: Revealed type is "Any"
Success: no issues found in 1 source file

## newest 3.x
» uv pip install -U prefect --pre
...
» mypy repros/task_typing.py
repros/task_typing.py:12: note: Revealed type is "Any"
Success: no issues found in 1 source file

is there anything you notice that I'm missing here?

[williamjamir]

Thanks for looking at this @zzstoatzz !

It's odd that mypy is not detecting the correct typing for you. The output of reveal_type is Any, which, in my understanding, disables the check that would be made on partial.

I would expected to see the reveal_type instead as Task, like in my initial message.

[zzstoatzz]

taking another look, I was able to reproduce in a completely fresh sandbox environment

(root) root@678e57987c9b:~# mypy /tmp/repros/14756.py
/tmp/repros/14756.py:11: error: "Task[[int, int], None]" not callable  [misc]
/tmp/repros/14756.py:12: note: Revealed type is "prefect.tasks.Task[[a: builtins.int, b: builtins.int], None]"
Found 1 error in 1 file (checked 1 source file)

will dig into this

[zzstoatzz]

it appears that I wasn't able to reproduce before because I had follow_imports = skip set, once I turned that off I could reliably reproduce.

I don't yet understand what mypy is on about here, since we overload __call__ for several cases (perhaps incorrectly somehow) so it should be recognized as a callable thing. (edit, its because of partial)

perhaps this issue is related? python/mypy#5079 (edit, I dont think it is)

---

edit actually it appears this might be more relevant python/mypy#17585

as without the partial, we pass fine. I would say for the moment, I think this is an upstream issue with mypy (as described in the above linked issue).