`__hash__ = None` generates an error

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
python
Domain
devtools

Research direction

No source file or test is named. First reproduce the snippet with mypy 0.550 and --strict-optional, then trace the handling of the hash assignment; done means the unhashable class is accepted without this incompatible-assignment error and a regression test covers it.

Written by the indexing model from the issue text.

Description

needs discussion priority-1-normal topic-strict-optional

In mypy 0.550 with --strict-optional, defining an unhashable class like so:

class Foo:
    __hash__ = None

gives

hash.py:2: error: Incompatible types in assignment (expression has type "None", base class "object" defined the type as "Callable[[object], int]")
Dominant language
Python
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Merged PRs (30d)
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