Question

I’m using Python’s subprocess.communicate() to read stdout from a process that runs for about a minute.

How can I print out each line of that process’s stdout in a streaming fashion, so that I can see the output as it’s generated, but still block on the process terminating before continuing?

subprocess.communicate() appears to give all the output at once.

Answer 1

Please note, I think J.F. Sebastian’s method (below) is better.

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Here is an simple example (with no checking for errors):

import subprocess
proc = subprocess.Popen('ls',
                       shell=True,
                       stdout=subprocess.PIPE,
                       )
while proc.poll() is None:
    output = proc.stdout.readline()
    print output,

If ls ends too fast, then the while loop may end before you’ve read all the data.

You can catch the remainder in stdout this way:

output = proc.communicate()[0]
print output,