Python 3.4：popen.communicate() 程序丢失后答案

【问题标题】：Python 3.4: After popen.communicate() program is lostPython 3.4：popen.communicate() 程序丢失后
【发布时间】：2016-12-20 14:32:02
【问题描述】：

我将尝试在我的 RPi 上连接一个按钮来控制 mplayer，第一次按下按钮将启动播放器，然后每次按下按钮将播放播放列表中的另一个条目。作为一个最小示例，我在 Linux Mint 18 和 Python3.4.3 上创建了以下脚本：

from time import sleep
from subprocess import Popen, PIPE, DEVNULL

cmd = ["mplayer", "-shuffle", "-playlist", "/path/to/playlist.m3u"]

if __name__ == '__main__':
    first = False
    p = None
    i = 0

    if first == False: # should simulate first button
        print("player starting")
        p = Popen(cmd, stdin=PIPE, stdout=DEVNULL)
        print("player started")
        first = True

    while 1:
        sleep(1)
        i += 1
        print(str(i)+ " " +str(first))

        if i == 5 and first == True: # should simulate each later button
            i = 0
            print("sending keystroke to mplayer")
            p.communicate(b"\n")[0] # mplayer plays next song, but the program is lost
            print("sended keystroke to mplayer - never printed")

输出是：

player starting
player started
1 True
2 True
3 True
4 True
5 True
sending keystroke to mplayer

现在我期待循环重启，但它不见了。调试对我没有帮助。你有什么想法如何解决问题以及如何返回循环？

谢谢。

【问题讨论】：

Popen.communicate() 尝试从 stdout 和 stderr 读取数据，直到 EOF 并等待进程终止。换句话说，它会一直阻塞，直到 mplayer 退出。

标签： python python-3.x subprocess popen

【解决方案1】：

我用 mplayer slave 解决了：

from time import sleep
from subprocess import Popen

pathtoControlFile = "/home/immi/mplayer-control"
cmd = ["mplayer", "-slave", "-input", "file="+pathtoControlFile, "-shuffle", "-playlist", "/media/immi/9A005723005705A3/Musik/playlist.m3u"]

if __name__ == '__main__':
    first = False
    i = 0

    if first == False:      # initial start
        print("player starting")
        p = Popen(cmd)
        print("player started")
        first = True

    while 1:
        sleep(1)
        i += 1
        print(str(i)+ " " +str(first))

        if i == 5 and first == True: # each later button
            i = 0
            print("sending keystroke to mplayer")
            with open(pathtoControlFile, "wb+", buffering=0) as fileInput:
                p = Popen(["echo", "pt_step next"], stdout=fileInput)

【讨论】：