Python Popen().stdout.read() hang

牧云@^-^@ 提交于 2020-03-17 08:46:27

问题


I'm trying to get output of another script, using Python's subprocess.Popen like follows

process = Popen(command, stdout=PIPE, shell=True)
exitcode = process.wait()
output = process.stdout.read()   # hangs here

It hangs at the third line, only when I run it as a python script and I cannot reproduce this in the python shell.

The other script prints just a few words and I am assuming that it's not a buffer issue.

Does anyone has idea about what I am doing wrong here?


回答1:


You probably want to use .communicate() rather than .wait() plus .read(). Note the warning about wait() on the subprocess documentation page:

Warning This will deadlock when using stdout=PIPE and/or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.

http://docs.python.org/2/library/subprocess.html#subprocess.Popen.wait




回答2:


read() waits for EOF before returning.

You can:

  • wait for the subprocess to die, then read() will return.
  • use readline() if your output is broken into lines (will still hang if no output lines).
  • use os.read(F,N) which returns at most N bytes from F, but will still block if the pipe is empty (unless O_NONBLOCK is set on the fd).



回答3:


You can see how to deal with hanging reading of stdout/stderr in the next sources:

readingproc



来源:https://stackoverflow.com/questions/14433712/python-popen-stdout-read-hang

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