Fix parsing of namespaced attributes with Python 3.8 in twisted.words.xish.domish.ExpatElementStream

src/twisted/words/newsfragments/9730.bugfix

@@ -0,0 +1 @@
+Fixed parsing of streams with Python 3.8 when there are spaces in namespaces or namespaced attributes in twisted.words.xish.domish.ExpatElementStream

src/twisted/words/test/test_domish.py

@@ -350,6 +350,23 @@ class DomishStreamTestsMixin:
             self.elements[0].attributes, {(" bar baz ", "baz"): "quux"})
 
 
+    def test_attributesWithNamespaces(self):
+        """
+        Attributes with namespace are parsed without Exception.
+        (https://twistedmatrix.com/trac/ticket/9730 regression test)
+        """
+
+        xml = b"""<root xmlns:test='http://example.org' xml:lang='en'>
+                    <test:test>test</test:test>
+                  </root>"""
+
+        # with Python 3.8 and without #9730 fix, the following error would
+        # happen at next line:
+        # ``RuntimeError: dictionary keys changed during iteration``
+        self.stream.parse(xml)
+        self.assertEqual(self.elements[0].uri, "http://example.org")
+
+
     def testChildPrefix(self):
         xml = b"<root xmlns='testns' xmlns:foo='testns2'><foo:child/></root>"
 

src/twisted/words/xish/domish.py

@@ -807,11 +807,18 @@ class ExpatElementStream:
             qname = ('', name)
 
         # Process attributes
+        newAttrs = {}
+        toDelete = []
         for k, v in attrs.items():
             if " " in k:
                 aqname = k.rsplit(" ", 1)
-                attrs[(aqname[0], aqname[1])] = v
-                del attrs[k]
+                newAttrs[(aqname[0], aqname[1])] = v
+                toDelete.append(k)
+
+        attrs.update(newAttrs)
+
+        for k in toDelete:
+            del attrs[k]
 
         # Construct the new element
         e = Element(qname, self.defaultNsStack[-1], attrs, self.localPrefixes)