code: def resolve_schema_instance(schema):
      
      if isinstance(schema, type) and issubclass(schema, marshmallow.Schema):
          return schema()
      if isinstance(schema, marshmallow.Schema):
          return schema
      try:
          return marshmallow.class_registry.get_class(schema)()
      except marshmallow.exceptions.RegistryError:
          raise ValueError(
              "{!r} is not a marshmallow.Schema subclass or instance and has not"
              " been registered in the Marshmallow class registry.".format(schema)
          )
docs: Return schema instance for given schema (instance or class)
  
      :param type|Schema|str schema: instance, class or class name of marshmallow.Schema
      :return: schema instance of given schema (instance or class)