Join computed suboptimally with multiple inheritance

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#4,373 6 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start with the reproducer in the issue body and run mypy on it. Trace list-literal type inference and multiple-inheritance handling; done means the revealed type preserves enough of Mix and Base for a.foo() to type-check, with regression coverage.

Written by the indexing model from the issue text.

Description

bug topic-inheritance 
class Base:
    def foo(self): pass

class Mix: pass

class A(Mix, Base): pass

class B(Mix, Base): pass

def foo() -> None:
    a = [A(), B()]
    reveal_type(a)  # Shows Mix
    a.foo()  # E: "Mix" has no attribute "foo"

Could we do something better here? Ideally the inferred type of a should be an anonymous subclass of Mix and Base.

Dominant language
Python
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Merged PRs (30d)
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