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Non-overlapping identity check when left operand is not optional and right operand is None #11888
Description
mypy does not complain on line 4 of this code:
i: int = 1
s: str = 'hi'
i is s # error: Non-overlapping identity check (left operand type: "int", right operand type: "str")
if i is None: # ok
...would it be possible to raise a Non-overlapping identity check error in that case, as in the previous line?
mypy version:
$ mypy --version
mypy 0.930
Activity
chnmasta05 commentedon May 31, 2023
I suggest adding the
topic-overlaplabel.It was decided when --strict-equality was implemented that (according to #6370) "X and None are overlapping even in strict-optional mode".
Current documentation reads:
gschaffner commentedon Nov 24, 2025
Is this the same as #18386?
hauntsaninja commentedon Oct 21, 2026
As chnmasta05 mentions, this is intentional in
--strict-equalitynot warning on the comparison.Note
--warn-unreachablewill warn about the dead code in your if block.