Measure traffic per second using /proc/net/dev

bandwidth.py

import time

last = 0L
while True:
        current = 0L
        lines = open("/proc/net/dev").readlines()[3:]
        for l in lines:
                ll = l.split()
                current += long(ll[1])+long(ll[9])
        delta = current - last
        last = current
        print "%s bytes per second" % delta
        time.sleep(1)