New to Python, help printing output of system calls

Expand Post »

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.

slendergreen

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

1 posts
since Aug 2008

Permalink

Aug 18th, 2008

Re: New to Python, help printing output of system calls

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.

slate

Reputation Points: 56

Solved Threads: 65

Posting Whiz in Training

Offline

242 posts
since Jun 2008

Permalink

Aug 18th, 2008

Re: New to Python, help printing output of system calls

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

python Syntax (Toggle Plain Text)
child = Popen(...)
for line in child.stdout:
  print line
child = Popen(...)
for line in child.stdout:
  print line

Gribouillis

Reputation Points: 930

Solved Threads: 666

Posting Maven

Offline

2,655 posts
since Jul 2008

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in Python Forum Timeline: Opening pipelines with python ?

Next Thread in Python Forum Timeline: Need Help With a Function....

DaniWeb Message

Cancel Changes

User Name
Password