python从SUMO中获取车辆平均行驶时间

<tripinfos>
    <tripinfo id="<VEHICLE_ID>" \
            depart="<DEPARTURE_TIME>" departLane="<DEPARTURE_LANE_ID>" \
            departPos="<DEPARTURE_POSITION>" departSpeed="<DEPARTURE_SPEED>" \
            departDelay="<DEPARTURE_DELAY>" \
            arrival="<ARRIVAL_TIME>" arrivalLane="<DEPARTURE_LANE_ID>" \
            arrivalPos="<ARRIVAL_POSITION>" arrivalSpeed="<ARRIVAL_SPEED>" \
            duration="<TRAVEL_TIME>" routeLength="<ROUTE_LENGTH>" \
            waitSteps="<STEPS_WITH_HALTS>" rerouteNo="<REROUTE_NUMBER>" \
            devices="<DEVICE_LIST>" vtype="<VEHICLE_TYPE_ID>"/>

   ... information about further vehicles ...

</tripinfos>

# -*- coding: utf-8 -*-
"""
Created on Thu Dec 03 18:50:50 2015

@author: Luyixiao
"""

import bs4
soup = bs4.BeautifulSoup(open('E:/averageTime.xml'))
soup = soup.body.tripinfos

list = []
for child in soup.children:
    list.append(child)

kk = list[0]
for i in range(0,len(list)):#delete the blank record
    if list[i]==kk:
        list.pop(i)
        
sum = 0
for t in list:#count the amount duration
    sum= sum+float(t['duration'])

average = sum/len(list)#calculate the average time for per vehicle