def _str_or_file(argument):
    """Helper type to parse a string as a file.

    This is because of the implementation of @<file> didn't work as expected originally,
    and this might not be the best practice way to do a cli application.
    """
    if argument.startswith('@'):
        with open(argument[1:], 'r') as f:
            output = ''.join(f.readlines())
    else:
        output = argument
    return output
