How to parse xml response


I am fairly new to mitmproxy, proxy/network related topics and also python. Though I am not so great at it, i managed to get some scripts started. I ran into a snag. Not sure if this is a mitmproxy issue or a python issue for me. Basically, what i am trying to accomplish is I want to parse the flow.response.body using regex. I am having a hard time because the response flow.response.body is an xml response. Here is an example of what i would like to do below. Can someone help me to do it the correct way?

Thank you

import xml.etree.ElementTree as ET
import re

def response(context, flow):
        requestUrl = flow.request.url
        if '' == requestUrl:
        				tree = ET.parse(flow.response.body)
        				root = tree.getroot()
        				responseString = ET.tostring(root).decode('utf-8')
        				parsedVal = re.findall(r'(?<=over.).*?(?=here)', responseString)
        				print('this is the paresed value ' + parsedVal)

Basically i want to campture and change the xml payload to an new xml. But I need to keep the rest of the xml request the same as the first xml request. Any one has a suggestion it would be appreciated.

Thank You