docs: def trunc(self, model, prompt, **fields):
          """
          Truncates fields values for the given model. Prompts for a new
          value if truncation occurs.
          """
          for field_name, value in fields.items():
              field = model._meta.get_field(field_name)
              max_length = getattr(field, "max_length", None)
              if not max_length:
                  continue
              elif not prompt:
                  fields[field_name] = value[:max_length]
                  continue
              while len(value) > max_length:
                  encoded_value = value.encode("utf-8")
                  new_value = input("The value for the field %s.%s exceeds "
                      "its maximum length of %s chars: %s\n\nEnter a new value "
                      "for it, or press return to have it truncated: " %
                      (model.__name__, field_name, max_length, encoded_value))
                  value = new_value if new_value else value[:max_length]
              fields[field_name] = value
          return fields