from xml.etree import ElementTree as ET
doc = ET.fromstring('''
<root xmlns="http://example.com" xmlns:pre="http://example.com/prefix">
  <a>1</a>
  <pre:b>2</pre:b>
</root>
''')
nsmap = {'': 'http://example.com', 'pre':'http://example.com/prefix'}
doc.find('.//a')  # finds nothing
doc.find('.//a', namespaces=nsmap)  # finds nothing
doc.find('.//{http://example.com}a')  # works, but yuck
doc.find('.//pre:b', namespaces=nsmap)  # this works, though