Python popen python.exe

Question

I'm rather puzzled by why the code below doesn't print stdout and exit, instead it hangs (on windows). Any reason why?

import subprocess
from subprocess import Popen

def main():
    proc = Popen(
        'C:/Python33/python.exe',
        stderr=subprocess.STDOUT,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE
    )
    proc.stdin.write(b'exit()\r\n')
    proc.stdin.flush()
    print(proc.stdout.read(1))

if __name__=='__main__':
    main()

falsetru · Accepted Answer · 2013-12-21 07:24:39Z

1

Replace the following:

proc.stdin.flush()

with:

proc.stdin.close()

Otherwise the subprocess python.exe will wait forever stdin to be closed.

Alternative: using communicate()

proc = Popen(...)
out, err = proc.communicate(b'exit()\r\n')
print(out)  # OR print(out[:1]) if you want only the first byte to be print.

edited Dec 21, 2013 at 7:24

answered Dec 21, 2013 at 7:13

falsetru

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3 Comments

simonzack Over a year ago

Nothing is printed then, python should at least write something to stdout.

falsetru Over a year ago

@simonzack, Because you didn't give anything except exit() to the interpreter.

falsetru Over a year ago

@simonzack, Try proc.stdin.write(b'print(123);exit()\r\n').

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