code: 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
docs: 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