mypy: Signature of “__getitem__” incompatible with supertype “Sequence”

I have a class that inherits from MutableSequence like this:

class QqTag(MutableSequence): def __init__(self): self._children = [] def __getitem__(self, idx: int) -> 'QqTag': return self._children[idx]

mypy complains that Signature of "__getitem__" incompatible with supertype "Sequence".

In Sequence, this method is defined as:

@abstractmethod def __getitem__(self, index): raise IndexError

So, what's the problem and why mypy isn't happy with my implementation?


As mentioned in comments, a typeof slice can also be passed.

This will make mypy happy (at least on my machine ;):

class QqTag(MutableSequence): def __init__(self): self._children = [] def __getitem__(self, idx: Union[int, slice]) -> 'QqTag': return self._children[idx]


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