Почему Pycharm не распознаёт .register?

import reprlib
from collections import abc

RE_WORD = re.compile(r'\w+')


class Sentence:
    def __init__(self, text: str):
        self.text = text
        self._words = RE_WORD.findall(text)

    def __len__(self):
        return len(self._words)

    def __getitem__(self, key):
        return self._words[key]

    def __repr__(self):
        return f'{type(self).__name__}(%s)' % reprlib.repr(self.text)


abc.Sequence.register(Sentence)  # type: ignore
sentence = Sentence('Lorem ipsum dolor sit amet, conSecond addiction elit')
print(isinstance(sentence, abc.Sequence))