packet = (
  '<packet><server><create_session>{}</login>'
  '<data><user_ip>{}</user_ip><source_server></source_server></data>'
  '</create_session></server></packet>'
).format(plesk_user, user_encoded_ip)

<Element 'packet' at 0x7f7de9757fc0>

<?xml version="1.0" encoding="UTF-8"?>
<packet version="1.6.3.3">
  <server>
    <create_session>
      <result>
        <status>ok</status>
        <id>ede520d0fc93ae7aa0524076d631fba2</id>
      </result>
    </create_session>
 </server>
</packet>