code: def _validate_iterable(iterable_type, value):
      
      if isinstance(value, six.string_types):
          msg = "Invalid iterable of type(%s): %s"
          raise ValidationError(msg % (type(value), value))
  
      try:
          return iterable_type(value)
      except TypeError:
          raise ValidationError("Invalid iterable: %s" % (value))
docs: Convert the iterable to iterable_type, or raise a Configuration
      exception.