bpo-30485: Re-allow empty strings in ElementPath namespace mappings since they might actually be harmless and unused (and thus went undetected previously). (#12830)

Author: scoder

Lib/test/test_xml_etree.py

@@ -2466,9 +2466,6 @@ def test_findall_different_nsmaps(self):
  nsmap = {'xx': 'X', None: 'Y'}
  self.assertEqual(len(root.findall(".//xx:b", namespaces=nsmap)), 2)
  self.assertEqual(len(root.findall(".//b", namespaces=nsmap)), 1)
- nsmap = {'xx': 'X', '': 'Y'}
- with self.assertRaisesRegex(ValueError, 'namespace prefix'):
- root.findall(".//xx:b", namespaces=nsmap)
 
  def test_bad_find(self):
  e = ET.XML(SAMPLE_XML)

Lib/xml/etree/ElementPath.py

@@ -275,8 +275,6 @@ def iterfind(elem, path, namespaces=None):
 
  cache_key = (path,)
  if namespaces:
- if '' in namespaces:
- raise ValueError("empty namespace prefix must be passed as None, not the empty string")
  if None in namespaces:
  cache_key += (namespaces[None],) + tuple(sorted(
  item for item in namespaces.items() if item[0] is not None))