type checking of member assigned with lambda
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Description
Bug Report
What this https://github.com/python/mypy/pull/13400 looks like it's supposed to fix is not working here.
To Reproduce
from typing import Callable
class C:
f: Callable[[int], bool] = staticmethod(lambda x: print(type(x)) or True)
c = C()
c.f(3)
class D:
f: Callable[[int], bool] = lambda x: print(type(x)) or True
d = D()
d.f(3)
Expected Behavior
The one that works correctly should not have a mypy error.
The one that doesn't work correctly should be found by mypy.
Actual Behavior
The first one, class C, works correctly, but mypy says it's wrong.
output:
<class 'int'>
mypy:
Incompatible types in assignment (expression has type "staticmethod[bool]", variable has type "Callable[[int], bool]") [assignment]
The second one, class D, fails, but mypy doesn't see any problem with it.
output:
Traceback (most recent call last):
File ...
d.f(3)
TypeError: <lambda>() takes 1 positional argument but 2 were given
Your Environment
- Mypy version used: 0.990+dev
- Python version used: 3.8
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the supplied Python 3.8 reproducer with the reported mypy version and compare the diagnostics for classes C and D. Trace mypy's handling of annotated class-member assignments involving lambda expressions and staticmethod; done means the valid C assignment is accepted and the invalid D binding is reported, with regression coverage for both cases.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100