def remove(self, event, subscriber):
        """
        Remove a subscriber for an event.

        :param event: The name of an event.
        :param subscriber: The subscriber to be removed.
        """
        subs = self._subscribers
        if event not in subs:
            raise ValueError('No subscribers: %r' % event)
        subs[event].remove(subscriber)

        Remove a subscriber for an event.

        :param event: The name of an event.
        :param subscriber: The subscriber to be removed.
        
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_vendor/distlib/util.py