import socket, struct, fcntl
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sockfd = sock.fileno()
SIOCGIFADDR = 0x8915

def get_ip(iface = 'eth0'):
    ifreq = struct.pack('16sH14s', iface, socket.AF_INET, '\x00'*14)
    try:
        res = fcntl.ioctl(sockfd, SIOCGIFADDR, ifreq)
    except:
        return None
    ip = struct.unpack('16sH2x4s8x', res)[2]
    return socket.inet_ntoa(ip)

print get_ip('eth1')