How to insert a CSV within xml element tag using Python?

Hi Team,
I have a CSV file which I have to read through and needs to insert the content within an XML file using Python ONLY ( as most of the code base we have in python only). I managed to find the first part, missing how to insert to XML under "specific" tags.

cat input.csv
Host,PUBLICIP,PRIVATEIP,RAC
hactive,10.47.47.196,427.47.47.196,01
hpassive,10.47.47.197,47.47.47.197,01
hutility,10.47.47.198,47.47.47.198,01
datanode1,10.47.47.199,47.47.47.199,01
datanode2,10.47.47.207,47.47.47.207,01
import os,sys
import csv
from xml.etree import ElementTree as ET

str = ""

with open('input.csv', mode='r') as csv_file:
    csv_reader = csv.DictReader(csv_file)
    for row in csv_reader:
        str += '<Host_name="' + row["Host"] + '" Private_Addr="' + row["PRIVATEIP"] + '" Public_Addr="' + row["PUBLICIP"] + '" RACK_NO="' + row["RAC"] + '"/> \n'
    print(str.rstrip())

I want to insert the above output in to the below XML, in between <HostNames>:

                        <HostNames>
                                <Host name="node3" Pvt_IPADDR="47.47.47.197" Pub_IPADDR="10.47.47.197" RACK_NO="01"/>
                                <! --- The string I formatted , I want to put here" -->
                        </HostNames>

Note: <HostNames> tag can be any where in the config.xml and new "str" I want to put to the end of <HostNames> only.

Any help, really appreciable.