Fix right_type precision

[jslambda]

This is a fix for #15534

Without this fix mypy reports error (Incompatible return value type (got "str | None", expected "str")) for the following cases:

def foo(x: Dict[str, str]) -> str: return x.get("a") or x.get("b", "c")
def bar(x: Dict[str, str]) -> str: return None or  x.get("c","d")

I would appreciate your feedback

Best regards,
Hamid Alavi Toussi

[JelleZijlstra]

Please add a new test case to clarify what this is fixing.

[jslambda]

Hi @JelleZijlstra
This is a fix for #15534
Which file in the mypy source would be a good place for adding a test case for this kind of problem?

[jslambda]

Hi @JelleZijlstra
I have added a test case:
99d9052

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sublime_debugger (https://github.com/daveleroy/sublime_debugger)
+ modules/ui/layout.py:156: error: Unsupported operand types for - ("None" and "float")  [operator]
+ modules/ui/layout.py:156: note: Left operand is of type "float | None"

[AlexWaygood]

Thanks for the PR @jslambda! I just closed #15534, as the issue with dict.get has been resolved by a recent typeshed change (python/typeshed#10293). Will this PR be useful for other reasons, do you think, or should it be closed?

[jslambda]

Hi @AlexWaygood . Thanks for the comment. I'm not aware of other cases which are fixed by this PR so the PR can be closed.
Is there any other PR for merging the typeshed fix to mypy? I can still reproduce the error on da1853f

[AlexWaygood]

Is there any other PR for merging the typeshed fix to mypy? I can still reproduce the error on da1853f

We do a typeshed sync once a fortnight. The next one is due in the next few days, so not long to wait!

Thanks for the contribution, @jslambda!