Blog / 2011 / May / 13

Popen and Django Dev Server

May 13, 2011

I have code that does this:

lCommand = ["hg","history", "-r", "%s:%s" % (pFrom, pTo)]
lProcess = subprocess.Popen(lCommand, stdin=subprocess.PIPE, stdout=subprocess.PIPE)

in a Django view. This is intended to get the mercurial history between two revision numbers so that it can be shown on a web page. When using the dev server, I'm quite often getting a blank page instead of my HTML, and for each page request the server outputs:

Django version 1.2.1, using settings 'dewsbury.settings'
Development server is running athttp://127.0.0.1:8000/
Quit the server with CONTROL-C.

This is happening on every request. If I comment out the code that does the Popen, it works fine.

The Popen command is completing fine, I can print out the output on each request, it's just that the dev server is returning a blank page back to the browser. This is on the Django 1.2.1 release.

I've had a wander around the bugs related to this and the ones I could find seems to be closed as duplicate, or closed worksforme.

Solution

The solution was simple, but odd.

At the top of my code that runs Popen, I was doing this:

import subprocess
import datetime
import paramiko, base64, select, time
import os

Changing this around so that os was imported before subprocess fixed the problem.

References

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