code: def has_length(ref_length):
      
      def has_length_(x):
          if len(x) == ref_length:
              return True
          else:
              raise WrongLength(wrong_value=x, ref_length=ref_length)
  
      has_length_.__name__ = 'length_equals_{}'.format(ref_length)
      return has_length_
docs: 'length equals' validation function generator.
      Returns a validation_function to check that `len(x) == ref_length`
  
      :param ref_length:
      :return: