From 6a412c94b6b68e7e3632562dc7358a12ffd1447f Mon Sep 17 00:00:00 2001
From: scoder <stefan_ml@behnel.de>
Date: Sat, 3 Oct 2020 08:07:07 +0200
Subject: bpo-41900: C14N 2.0 serialisation failed for unprefixed attributes
 when a default namespace was defined. (GH-22474)

---
 Lib/xml/etree/ElementTree.py | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'Lib/xml/etree')

diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index da2bcad0b4..7a269001d6 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -1876,6 +1876,11 @@ class C14NWriterTarget:
                 self._declared_ns_stack[-1].append((uri, prefix))
                 return f'{prefix}:{tag}' if prefix else tag, tag, uri
 
+        if not uri:
+            # As soon as a default namespace is defined,
+            # anything that has no namespace (and thus, no prefix) goes there.
+            return tag, tag, uri
+
         raise ValueError(f'Namespace "{uri}" is not declared in scope')
 
     def data(self, data):
-- 
cgit v1.2.1