code: def _get_all(self, _type):
          
          if _type not in self.modules:
              raise ValueError("No such module, %s" % _type)
          if not self.insts_implementing.get(_type, None):
              raise ValueError("No instance implementing %s" % _type)
          return self.insts_implementing[_type]
docs: Gets all instances implementing type <_type>