docs: def RetryQuestion(question_text, output_re="", default_val=None):
    """Continually ask a question until the output_re is matched."""
    while True:
      if default_val is not None:
        new_text = "%s [%s]: " % (question_text, default_val)
      else:
        new_text = "%s: " % question_text
      # pytype: disable=wrong-arg-count
      output = builtins.input(new_text) or str(default_val)
      # pytype: enable=wrong-arg-count
      output = output.strip()
      if not output_re or re.match(output_re, output):
        break
      else:
        print("Invalid input, must match %s" % output_re)
    return output