Non-overlapping identity check when left operand is not optional and right operand is None

[sami-evangelista]

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

[chnmasta05]

I suggest adding the topic-overlap label.

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:

* X and None are overlapping even in strict-optional mode. This is to allow
'assert x is not None' for x defined as 'x = None  # type: str' in class body
(otherwise mypy itself would have couple dozen errors because of this).