u"""
    Check whether the value as argument be included the following list.
    ['ltsv', 'combined']

def is_log_format(value):
    u"""
    Check whether the value as argument be included the following list.
    ['ltsv', 'combined']
    """

    log_levels = ['ltsv', 'combined']

    if value in log_levels:
        return value

    else:
        err_message = ('"log_format" supported following value: '
                       '{0}'.format(log_levels)
                       )
        raise validate.VdtValueError(err_message)