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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def error_message():
 """ Writes out error message specifying the valid commands. Returns: Failure code for system exit """

    sys.stderr.write('valid commands:\n')
    for cmd in get_valid_commands():
        sys.stderr.write('\t%s\n' % cmd)
    return -1