Sometimes we have more than one net interface.
A simple method to find out the mac address of a specific interface, is:
def getmac(interface):
try:
mac = open('/sys/class/net/'+interface+'/address').readline()
except:
mac = "00:00:00:00:00:00"
return mac[0:17]
to call the method is simple
myMAC = getmac("wlan0")