code: def _assert_is_type(name, value, value_type):
      
      if not isinstance(value, value_type):
          if type(value_type) is tuple:
              types = ', '.join(t.__name__ for t in value_type)
              raise ValueError('{0} must be one of ({1})'.format(name, types))
          else:
              raise ValueError('{0} must be {1}'
                               .format(name, value_type.__name__))
docs: Assert that a value must be a given type.