def _FindUSBDevices(self):
    for item in self._GetDataTypeItems('usb'):
      if 'host_controller' in item:
        for usb_item in item.get('_items', []):
          if usb_item['_name'].find('iSight') > -1:
            self._profile['isight_serial_number'] = (
                usb_item.get('d_serial_num', 'unknown'))
Find all USB devices.
dataset/ETHPy150Open google/simian/src/simian/mac/common/hw.py/SystemProfile._FindUSBDevices