pylint warning E1101 "instance of 'object' has no replace member"

This is my code:

class MyClass(object):
    __metaclass__ = Singleton

    def __init__(self):

        self._data = {
            'some_value': string_value
        }

    def get_value(self):
        return self._data['some_value'].replace('"', '')

So I just want to return value with " character deleted. String value has type class 'str'. But now I always get pylint E1101 warning "instance of 'object' has no replace member". Why does it appear and how can I fix it?