'\'type\' should be OFPAT_SET_NW_SRC or OFPAT_SET_NW_DST'

def __init__(self, type=None, nw_addr=None):

    self.type = type
    if (nw_addr is not None):
        self.nw_addr = IPAddr(nw_addr)
    else:
        self.nw_addr = IPAddr(0)
