Arcpy update value in field based on value in another field

I am creating a level of service tool and i need to update the number of lanes field based on the operation type of the road. what i need it to do is if the operationtpe equal 2W then the number of lanes needs to be divided by 2

for row in rows:
    for field in fields:
        if optype == "2W"
        arcpy.getValue(lanes / 2)