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Mypy does not recognize missing method #6990
Description
In the following example, mypy does not catch that self.meh() does not exist. Is this expected behavior because of the static False?
class TestCase:
def foo(self) -> bool:
return False and self.meh()The original bug in our code base was harder to spot than this but it boils down to the same reason so I'm wondering if this is expected behavior.
If I change the example to
class TestCase:
def foo(self) -> bool:
return True and self.meh()then mypy does in fact spot the missing meh method.
mypy_bug.py:5: error: "TestCase" has no attribute "meh"
Activity
JelleZijlstra commentedon Jun 13, 2019
Mypy doesn't type check code it thinks is unreachable. I'm personally not convinced that's the right behavior, because it can lead to hard-to-debug issues, but that's probably not something we can easily change.
cburgdorf commentedon Jun 14, 2019
Hey @JelleZijlstra thank you for your prompt reply!
Yep, that's really unfortunate. In real code, these things can be far more subtle. The root cause in our case was a missing
@propertydecorator as seen below.If you add the
propertydecorator, mypy will rightfully catch the missingmeh()method but if you forget the property, the missing method just goes unnoticed.ilevkivskyi commentedon Jun 15, 2019
One of the possible ways forward is to emit an error/warning when mypy skips some branch because it is unreachable, see #2395
ilevkivskyi commentedon Jun 17, 2019
Now that we have a dedicated issue #7008, I think we can close this as a duplicate.