binder is too optimistic about refining attribute types in methods

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers

Research direction

Start by reproducing the strict-optional example in the issue and trace the binder's attribute-type refinement across the call to set_bar_to_none. Identify how method calls affect the narrowed type, then add or update the relevant type-checking coverage so this unsafe return is no longer accepted.

Written by the indexing model from the issue text.

Description

false-positive feature needs discussion priority-1-normal topic-literal-types

This example typechecks in strict-optional mode, but it is not type safe:

from typing import Optional 
 
 
class Foo: 
    bar: Optional[int] 
 
    def thing(self) -> int: 
        if self.bar is None: 
            return 0 
        self.set_bar_to_none() 
        return self.bar 
 
    def set_bar_to_none(self) -> None: 
        self.bar = None
Dominant language
Python
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Merged PRs (30d)
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