Member Avatar for slendergreen

I'm new to Python and not anywhere near a competent programmer.

Anyway, if someone could help me get over this hump, I'd appreciate it.

I need to write a Python script that calls commands from the OS that may have lengthy output. Let's say I want to see the results of an rsync between two directories. I'd like to print the output in real-time to a web page.

My web page calls the Python script. No problem.
My Python script does a system call to rsync. No problem.

Here's were I get puzzled. No output from the rsynch makes it to the screen. It runs, but I can't see that anything is happening until the rsync is finished.

What would be the correct technique for doing this kind of thing? Basically I want to call system functions and have their status output appear just as I would have seen it from the command line.

Thanks for any tips.

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Member Avatar for slate

Try subprocess.Popen stdout redirection to a file or to the web server input.

However I would not expose a long running server process via web. I think it would be better to schedule the process and present the output.

Member Avatar for Gribouillis

It would be easier if we could see the python line which runs the system call.
A possible solution to your problem is to start the system call without waiting for it's completion, using subprocess.Popen (see http://docs.python.org/lib/node533.html). Then, once you have a child process running, print it's output with a loop, like this

child = Popen(...)
for line in child.stdout:
  print line
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