How can I tell whether screen is running?

I am trying to run a Python program to see if the screen program is running. If it is, then the program should not run the rest of the code. This is what I have and it's not working:

#!/usr/bin/python

import os
var1 = os.system ('screen -r > /root/screenlog/screen.log')
fd = open("/root/screenlog/screen.log")
content = fd.readline()

while content:
 if content == "There is no screen to be resumed.":
  os.system ('/etc/init.d/tunnel.sh')
  print "The tunnel is now active."
 else:
  print "The tun开发者_StackOverflow社区nel is running."
fd.close()

I know there are probably several things here that don't need to be and quite a few that I'm missing. I will be running this program in cron.

---

from subprocess import Popen, PIPE

def screen_is_running():
    out = Popen("screen -list",shell=True,stdout=PIPE).communicate()[0]
    return not out.startswith("This room is empty")

---

Maybe the error message that you redirect on the first os.system call is written on the standard error instead of the standard output. You should try replacing this line with:

var1 = os.system ('screen -r 2> /root/screenlog/screen.log')

Note the 2> to redirect standard error to your file.