<?xml version="1.0" encoding="UTF-8"?>
    <root>
        <Result RC="0" />
        <Invoices>
            <Invoice Invoice_ID="12123" Invoice_Owner_ID="232" ICN_ID="2321" ICN_Owner_ID="321" Receipt_Date="15.12.2016">
              <Receiver CompanyName="com1" ContactName="name1" Address="adr1" />
              <Shipper CompanyName="com2" Address="adr2" />
            </Invoice>
            <Invoice Invoice_ID="23232" Invoice_Owner_ID="32" ICN_ID="3213" ICN_Owner_ID="32" Receipt_Date="15.12.2016">
              <Receiver CompanyName="com3" ContactName="name2" Address="adr3" />
              <Shipper CompanyName="com4" Address="adr4" />
            </Invoice>
        </Invoices>
    </root>

Начало скрипта

import xml.etree.ElementTree as ET

tree = ET.parse("test.xml")
root = tree.getroot()


for elem in root.iter('Invoice'):
    invoice_id = elem.get('Invoice_ID')
    invoice_owner_id = elem.get('Invoice_Owner_ID')
    icn_id = elem.get('ICN_ID')
    icn_owner_id = elem.get('ICN_Owner_ID')
    receipt_date = elem.get('Receipt_Date')
    print(invoice_id, invoice_owner_id, icn_id, icn_owner_id, receipt_date)