net.py

#!/usr/bin/env Python

import time
import sys

if len(sys.argv) > 1:
    INTERFACE = sys.argv[1]
else:
    INTERFACE = 'eth1'
STATS = []
print 'Interface:',INTERFACE

def rx():
    ifstat = open('/proc/net/dev').readlines()
    for interface in  ifstat:
        #print '----', interface, '-----'
        if INTERFACE in interface:
            stat = float(interface.split()[1])
            STATS[0:] = [stat]

def tx():
    ifstat = open('/proc/net/dev').readlines()
    for interface in  ifstat:
        if INTERFACE in interface:
            stat = float(interface.split()[9])
            STATS[1:] = [stat]

print   'In         Out'
rx()
tx()

while   True:
    time.sleep(1)
    rxstat_o = list(STATS)
    rx()
    tx()
    RX = float(STATS[0])
    RX_O = rxstat_o[0]
    TX = float(STATS[1])
    TX_O = rxstat_o[1]
    RX_RATE = round((RX - RX_O)/1024/1024,3)
    TX_RATE = round((TX - TX_O)/1024/1024,3)
    print RX_RATE ,'MB      ',TX_RATE ,'MB'