'Get an instance of an IE with name ie_key, it will try to get one from
the _ies list, if there\'s no instance it will create a new one and add
it to the extractor list.'

def get_info_extractor(self, ie_key):

    ie = self._ies_instances.get(ie_key)
    if (ie is None):
        ie = get_info_extractor(ie_key)()
        self.add_info_extractor(ie)
    return ie
