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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 eval_stdin():
    'evaluate expressions read from stdin'
    cmd = ['plash', 'eval']
    p = subprocess.Popen(cmd, stdin=sys.stdin, stdout=sys.stdout)
    exit = p.wait()
    if exit:
        raise subprocess.CalledProcessError(exit, cmd)