Issue #25902: Fixed various refcount issues in ElementTree iteration.

2 files changed, 57 insertions, 4 deletions

diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index 57d8e4d..358484d 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -1666,6 +1666,57 @@ class BugsTest(unittest.TestCase):
         ET.register_namespace('test10777', 'http://myuri/')
         ET.register_namespace('test10777', 'http://myuri/')
 
+    def test_lost_text(self):
+        # Issue #25902: Borrowed text can disappear
+        class Text:
+            def __bool__(self):
+                e.text = 'changed'
+                return True
+
+        e = ET.Element('tag')
+        e.text = Text()
+        i = e.itertext()
+        t = next(i)
+        self.assertIsInstance(t, Text)
+        self.assertIsInstance(e.text, str)
+        self.assertEqual(e.text, 'changed')
+
+    def test_lost_tail(self):
+        # Issue #25902: Borrowed tail can disappear
+        class Text:
+            def __bool__(self):
+                e[0].tail = 'changed'
+                return True
+
+        e = ET.Element('root')
+        e.append(ET.Element('tag'))
+        e[0].tail = Text()
+        i = e.itertext()
+        t = next(i)
+        self.assertIsInstance(t, Text)
+        self.assertIsInstance(e[0].tail, str)
+        self.assertEqual(e[0].tail, 'changed')
+
+    def test_lost_elem(self):
+        # Issue #25902: Borrowed element can disappear
+        class Tag:
+            def __eq__(self, other):
+                e[0] = ET.Element('changed')
+                next(i)
+                return True
+
+        e = ET.Element('root')
+        e.append(ET.Element(Tag()))
+        e.append(ET.Element('tag'))
+        i = e.iter('tag')
+        try:
+            t = next(i)
+        except ValueError:
+            self.skipTest('generators are not reentrant')
+        self.assertIsInstance(t.tag, Tag)
+        self.assertIsInstance(e[0].tag, str)
+        self.assertEqual(e[0].tag, 'changed')
+
 
 # --------------------------------------------------------------------
 
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 62b5d3a..b4e110d 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -428,12 +428,14 @@ class Element:
         tag = self.tag
         if not isinstance(tag, str) and tag is not None:
             return
-        if self.text:
-            yield self.text
+        t = self.text
+        if t:
+            yield t
         for e in self:
             yield from e.itertext()
-            if e.tail:
-                yield e.tail
+            t = e.tail
+            if t:
+                yield t
 
 
 def SubElement(parent, tag, attrib={}, **extra):