NM_task_2.py

import xmltodict

xml = """
<feed xml:lang='en'>
    <title>NPBFX</title>
    <subtitle lang='en'>Programming challenges
    </subtitle>
    <link rel='alternate' type='text/html' href='http://npbfx.com/' />
    <updated>2020-10-28T12:00:00</updated>
</feed>
"""

xml_dict = xmltodict.parse(xml, xml_attribs = False)
print (xml_dict)

def depth(d):
    if isinstance(d, dict):
        return 1 + (max(map(depth, d.values())) if d else 0)
    return 0

print (depth(xml_dict)-1)