docs: def validate(self, value):
          """Validate the length of a list.
  
          :param value: List of values.
  
          :raises: :class:`halogen.exception.ValidationError` exception when length of the list is less than
              minimum or greater than maximum.
          """
          try:
              length = len(value)
          except TypeError:
              length = 0
  
          if self.min_length is not None:
              min_length = self.min_length() if callable(self.min_length) else self.min_length
              if length < min_length:
                  raise exceptions.ValidationError(self.min_err.format(min_length))
  
          if self.max_length is not None:
              max_length = self.max_length() if callable(self.max_length) else self.max_length
              if length > max_length:
                  raise exceptions.ValidationError(self.max_err.format(max_length))