#10777: fix iteration over dict keys while mutating the dict.

Lib/test/test_xml_etree.py

@@ -1841,6 +1841,15 @@ def check_issue6565():
 
     """
 
+def check_issue10777():
+    """
+    Registering a namespace twice caused a "dictionary changed size during
+    iteration" bug.
+
+    >>> ET.register_namespace('test10777', 'http://myuri/')
+    >>> ET.register_namespace('test10777', 'http://myuri/')
+    """
+
 # --------------------------------------------------------------------
 
 

Lib/xml/etree/ElementTree.py

@@ -1068,7 +1068,7 @@ _serialize = {
 def register_namespace(prefix, uri):
     if re.match("ns\d+$", prefix):
         raise ValueError("Prefix format reserved for internal use")
-    for k, v in _namespace_map.items():
+    for k, v in list(_namespace_map.items()):
         if k == uri or v == prefix:
             del _namespace_map[k]
     _namespace_map[uri] = prefix

Misc/NEWS

@@ -18,6 +18,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #10777: Fix "dictionary changed size during iteration" bug in
+  ElementTree register_namespace().
+
 - Issue #10626: test_logging now preserves logger disabled states.
 
 - Issue #10774: test_logging now removes temp files created during tests.