Obtener la cantidad de Bytes transferidos

Imprime la cantidad de datos en Bytes transferidos en la interfaz indicada. 

interface= 'eth0'
for line in open('/proc/net/dev', 'r'):
    if interface in line:
        data = line.split('%s:' % interface)[1].split()
        rx_bytes, tx_bytes = (data[0], data[8])
print '%s bytes received' % rx_bytes
print '%s bytes sent' % tx_bytes

Ejemplo: 

juan@maverick:~$ /usr/bin/env python prueba.py
2066696798 bytes received
169266445 bytes sent

USLA