gh-140601: Add ResourceWarning to iterparse when not closed

Doc/library/xml.etree.elementtree.rst

@@ -656,6 +656,10 @@ Functions
    .. versionchanged:: 3.13
       Added the :meth:`!close` method.
 
+   .. versionchanged:: 3.15
+      A :exc:`ResourceWarning` is now emitted if the iterator opened a file
+      and is not explicitly closed.
+
 
 .. function:: parse(source, parser=None)
 

Lib/test/test_xml_etree.py

@@ -698,22 +698,39 @@ def test_iterparse(self):
             self.assertEqual(str(cm.exception),
                     'junk after document element: line 1, column 12')
             del cm, it
+            gc_collect()
+
+        with self.assertRaises(FileNotFoundError):
+            iterparse("nonexistent")
+
+    def test_iterparse_not_close(self):
+        # Not closing before del should emit ResourceWarning
+        iterparse = ET.iterparse
 
         # Not exhausting the iterator still closes the resource (bpo-43292)
-        with warnings_helper.check_no_resource_warning(self):
+        with self.assertWarns(ResourceWarning) as wm:
             it = iterparse(SIMPLE_XMLFILE)
             del it
+            gc_collect()
+        self.assertIn('unclosed file', str(wm.warning))
+        self.assertIn(repr(SIMPLE_XMLFILE), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
 
+        # Explicitly calling close() should not emit warning
         with warnings_helper.check_no_resource_warning(self):
             it = iterparse(SIMPLE_XMLFILE)
             it.close()
             del it
 
-        with warnings_helper.check_no_resource_warning(self):
+        with self.assertWarns(ResourceWarning) as wm:
             it = iterparse(SIMPLE_XMLFILE)
             action, elem = next(it)
             self.assertEqual((action, elem.tag), ('end', 'element'))
             del it, elem
+            gc_collect()
+        self.assertIn('unclosed file', str(wm.warning))
+        self.assertIn(repr(SIMPLE_XMLFILE), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
 
         with warnings_helper.check_no_resource_warning(self):
             it = iterparse(SIMPLE_XMLFILE)
@@ -722,9 +739,6 @@ def test_iterparse(self):
             self.assertEqual((action, elem.tag), ('end', 'element'))
             del it, elem
 
-        with self.assertRaises(FileNotFoundError):
-            iterparse("nonexistent")
-
     def test_iterparse_close(self):
         iterparse = ET.iterparse
 

Lib/xml/etree/ElementTree.py

@@ -1255,22 +1255,28 @@ def iterator(source):
             if it is not None:
                 it.root = root
         finally:
+            nonlocal close_source
             if close_source:
                 source.close()
+                close_source = False
 
     gen = iterator(source)
     class IterParseIterator(collections.abc.Iterator):
         __next__ = gen.__next__
+
         def close(self):
+            nonlocal close_source
             if close_source:
                 source.close()
             gen.close()
+            close_source = False
 
-        def __del__(self):
-            # TODO: Emit a ResourceWarning if it was not explicitly closed.
-            # (When the close() method will be supported in all maintained Python versions.)
+        def __del__(self, _warn=warnings.warn):
             if close_source:
-                source.close()
+                try:
+                    _warn(f"unclosed file {source.name!r}", ResourceWarning, stacklevel=2)
+                finally:
+                    source.close()
 
     it = IterParseIterator()
     it.root = None

Misc/NEWS.d/next/Library/2025-10-25-22-55-07.gh-issue-140601.In3MlS.rst

@@ -0,0 +1,4 @@
+:func:`xml.etree.ElementTree.iterparse` now emits a :exc:`ResourceWarning`
+when the iterator is not explicitly closed and was opened with a filename.
+This helps developers identify and fix resource leaks. Patch by Osama
+Abdelkader.