'Create a new YadisService Manager for this starting URL and
suffix, and store it in the session.
@raises KeyError: When I already have a manager.
@return: A new YadisServiceManager or None'

def createManager(self, services, yadis_url=None):

    key = self.getSessionKey()
    if self.getManager():
        raise KeyError(('There    is    already    a    %r    manager    for    %r' % (key, self.url)))
    if (not services):
        return None
    manager = YadisServiceManager(self.url, yadis_url, services, key)
    manager.store(self.session)
    return manager
