How to use the xblock.runtime.KeyValueStore.Key function in XBlock

def _user_state_key(self):
        return xblock.runtime.KeyValueStore.Key(
            scope=xblock.fields.Scope.user_state, user_id='123',
            block_scope_id='456', field_name='my_field')

if block_scope == BlockScope.ALL:
                block_id = None
            elif block_scope == BlockScope.USAGE:
                block_id = block.scope_ids.usage_id
            elif block_scope == BlockScope.DEFINITION:
                block_id = block.scope_ids.def_id
            elif block_scope == BlockScope.TYPE:
                block_id = block.scope_ids.block_type

            if field.scope.user == UserScope.ONE:
                user_id = block.scope_ids.user_id
            else:
                user_id = None

        key = KeyValueStore.Key(
            scope=field.scope,
            user_id=user_id,
            block_scope_id=block_id,
            field_name=name,
            block_family=block.entry_point,
        )
        return key