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Possible truthy-bool false positive with := #15685
Description
Consider this code with truthy-bool:
class A:
def method(self) -> bool:
return True # whatever
if (a := A()) and a.method():
print(a)It will output:
» mypy ex.py --enable-error-code=truthy-bool
ex.py:6: error: "ex.a" has type "A" which does not implement __bool__ or __len__ so it could always be true in boolean context [truthy-bool]
ex.py:6: error: "ex.A" returns "A" which does not implement __bool__ or __len__ so it could always be true in boolean context [truthy-bool]
Two questions:
- Why two errors?
- Maybe we should skip this rule completely for
(:=) and ..., becauseais not really the main thing we check here?
CC @ikonst
Activity
[-]Possible `thruthy-bool` false positive with `:=`[/-][+]Possible `truthy-bool` false positive with `:=`[/+]AlexWaygood commentedon Jul 15, 2023
I think it would probably be better to emit one error rather than two here. But I don't think I agree that it's a false positive. The first side of the left operand will always evaluate to
True, so you could write the snippet more simply as:ikonst commentedon Jul 15, 2023
Agree with (1), need to look into it.
Don't see compelling evidence to special-case (2). This code uses
andcreatively as a statement separator (since lhs is always true), and I'm not convinced this is idiomatic or common (just browsed over examples in PEP-572 but I might've missed something).Suppress second error message with `:=` and `[truthy-bool]` (python#1…