i use this:

import re

match = re.search('threshold of high utilization [^:]+: current value ([\d\.]+)', evt.message)

if match and device:

    ifaces = [ i for i in device.os.interfaces() if i.name() == evt.component ]

    if len(ifaces) > 0:

        current = float(match.groups()[0]) * 8

        speed = ifaces[0].speed

        util = (current / speed) * 100

        evt.summary = "Network interface utilization at %3.1f%%" % (util,)

same here... but weird thing for me is that it works for some devices but not others. All devices are Cisco though.