Getting realtime output using subprocess

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I am trying to write a wrapper script for a command line program (svnadmin verify) that will display a nice progress indicator for the operation. This requires me to be able to see each line of output from the wrapped program as soon as it is output.

I figured that I"d just execute the program using subprocess.Popen, use stdout=PIPE, then read each line as it came in and act on it accordingly. However, when I ran the following code, the output appeared to be buffered somewhere, causing it to appear in two chunks, lines 1 through 332, then 333 through 439 (the last line of output)

from subprocess import Popen, PIPE, STDOUT

p = Popen("svnadmin verify /var/svn/repos/config", stdout = PIPE, 
        stderr = STDOUT, shell = True)
for line in p.stdout:
    print line.replace("
", "")

After looking at the documentation on subprocess a little, I discovered the bufsize parameter to Popen, so I tried setting bufsize to 1 (buffer each line) and 0 (no buffer), but neither value seemed to change the way the lines were being delivered.

At this point I was starting to grasp for straws, so I wrote the following output loop:

while True:
    try:
        print p.stdout.next().replace("
", "")
    except StopIteration:
        break

but got the same result.

Is it possible to get "realtime" program output of a program executed using subprocess? Is there some other option in Python that is forward-compatible (not exec*)?

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Getting realtime output using subprocess __del__: Questions

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

from time import sleep
sleep(0.1) # Time in seconds

Getting realtime output using subprocess __del__: Questions

We hope this article has helped you to resolve the problem. Apart from Getting realtime output using subprocess, check other __del__-related topics.

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