在不中断管道的情况下与一个进程多次通信? [英] Communicate multiple times with a process without breaking the pipe?

问题描述

这不是我第一次遇到这个问题，而且确实困扰着我. 每当我使用Python subprocess模块打开管道时，如文档指定的那样，我只能使用它communicate一次:Read data from stdout and stderr, until end-of-file is reached

It's not the first time I'm having this problem, and it's really bugging me. Whenever I open a pipe using the Python subprocess module, I can only communicate with it once, as the documentation specifies: Read data from stdout and stderr, until end-of-file is reached

proc = sub.Popen("psql -h darwin -d main_db".split(),stdin=sub.PIPE,stdout=sub.PIPE)
print proc.communicate("select a,b,result from experiment_1412;\n")[0]
print proc.communicate("select theta,zeta,result from experiment_2099\n")[0]

这里的问题是Python第二次不高兴.确实，他决定在第一次交流后关闭文件:

The problem here is that the second time, Python isn't happy. Indeed, he decided to close the file after the first communicate:

Traceback (most recent call last):
File "a.py", line 30, in <module>
    print proc.communicate("select theta,zeta,result from experiment_2099\n")[0]
File "/usr/lib64/python2.5/subprocess.py", line 667, in communicate
    return self._communicate(input)
File "/usr/lib64/python2.5/subprocess.py", line 1124, in _communicate
     self.stdin.flush()
ValueError: I/O operation on closed file

是否允许进行多种通讯?

Are multiple communications allowed?

推荐答案

我认为您误会了沟通...

I think you misunderstand communicate...

http://docs.python.org/library/subprocess. html#subprocess.Popen.communicate

communicate向另一个进程发送一个字符串，然后等待它完成...(就像您说的那样，等待EOF监听stdout& stderror)

communicate sends a string to the other process and then waits on it to finish... (Like you said waits for the EOF listening to the stdout & stderror)

相反，您应该做的是:

proc.stdin.write('message')

# ...figure out how long or why you need to wait...

proc.stdin.write('message2')

(如果需要获取stdout或stderr，则可以使用proc.stdout或proc.stderr)

(and if you need to get the stdout or stderr you'd use proc.stdout or proc.stderr)

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