RegEx(Regular Expression) can be used to parse to parse Salesforce Login SOAP Response in Python.

Sample Code:

import re
strXMLString = '''<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns="urn:enterprise.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <soapenv:Body>
      <loginResponse>
         <result>
            <metadataServerUrl>https://infallibletechie.my.salesforce.com/services/Soap/m/29.0/00Di0000000icUB</metadataServerUrl>
            <passwordExpired>false</passwordExpired>
            <sandbox>false</sandbox>
            <serverUrl>https://infallibletechie.my.salesforce.com/services/Soap/c/29.0/00Di0000000icUB/0DFi00000008UYO</serverUrl>
            <sessionId>SampleSessionId</sessionId>
            <userId>005i0000002MUqLAAK</userId>
            <userInfo>
               <accessibilityMode>false</accessibilityMode>
               <currencySymbol>$</currencySymbol>
               <orgAttachmentFileSizeLimit>5242880</orgAttachmentFileSizeLimit>
               <orgDefaultCurrencyIsoCode>USD</orgDefaultCurrencyIsoCode>
               <orgDisallowHtmlAttachments>false</orgDisallowHtmlAttachments>
               <orgHasPersonAccounts>false</orgHasPersonAccounts>
               <organizationId>00Di0000000icUBKDI</organizationId>
               <organizationMultiCurrency>false</organizationMultiCurrency>
               <organizationName>InfallibleTechie</organizationName>
               <profileId>00ei0000001CMKcAAO</profileId>
               <roleId xsi:nil="true" />
               <sessionSecondsValid>6000</sessionSecondsValid>
               <userDefaultCurrencyIsoCode xsi:nil="true" />
               <userEmail>[email protected]</userEmail>
               <userFullName>TestUser</userFullName>
               <userId>005i0000002MUqLAAK</userId>
               <userLanguage>en_US</userLanguage>
               <userLocale>en_US</userLocale>
               <userName>[email protected]</userName>
               <userTimeZone>America/Los_Angeles</userTimeZone>
               <userType>Standard</userType>
               <userUiSkin>Theme3</userUiSkin>
            </userInfo>
         </result>
      </loginResponse>
   </soapenv:Body>
</soapenv:Envelope>''';
organizationId = re.findall( "<organizationId>(.*?)</organizationId>", strXMLString )[ 0 ];
print( 'Organization Id is', organizationId );
serverUrl = re.findall( "<serverUrl>(.*?)</serverUrl>", strXMLString )[ 0 ];
print( 'Server URL is', serverUrl );
strURL = re.findall( "(.*?)services/Soap", serverUrl )[ 0 ];
print( 'strURL is', strURL );

Output: