def pad(source: str, pad_len: int, align: str) -> str:
    """Return a padded string.

    :param source: The string to be padded.
    :param pad_len: The total length of the string to be returned.
    :param align: The alignment for the string.
    :return: The padded string.
    """
    return "{s:{a}{n}}".format(s=source, a=align, n=pad_len)