def METHOD_NAME(self, house):
    if house == 'house-of-lords':
        mships = [m for m in self.memberships if 'organization_id' in m and m['organization_id'] == house]
    else:
        mships = [m for m in self.memberships if 'post_id' in m and self.data.posts[m['post_id']]['organization_id'] == house]
    return Memberships(mships, self.data)