code: def hydrate(cls, db, limit):
          
  
          # Extract the limit name from the keyword arguments
          cls_name = limit.pop('limit_class')
  
          # Is it in the registry yet?
          if cls_name not in cls._registry:
              utils.find_entrypoint(None, cls_name)
  
          # Look it up in the registry
          cls = cls._registry.get(cls_name)
  
          # Instantiate the thing
          return cls(db, **limit) if cls else None
docs: Given a limit dict, as generated by dehydrate(), generate an
          appropriate instance of Limit (or a subclass).  If the
          required limit class cannot be found, returns None.