gh-140601: Add ResourceWarning to iterparse when not closed (GH-140603)

When iterparse() opens a file by filename and is not explicitly closed,
emit a ResourceWarning to alert developers of the resource leak.

Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Doc/library/xml.etree.elementtree.rst

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

Doc/whatsnew/3.15.rst

@@ -1244,3 +1244,9 @@ that may require changes to your code.
 
 * :meth:`~mmap.mmap.resize` has been removed on platforms that don't support the
   underlying syscall, instead of raising a :exc:`SystemError`.
+
+* Resource warning is now emitted for unclosed
+  :func:`xml.etree.ElementTree.iterparse` iterator if it opened a file.
+  Use its :meth:`!close` method or the :func:`contextlib.closing` context
+  manager to close it.
+  (Contributed by Osama Abdelkader and Serhiy Storchaka in :gh:`140601`.)

Lib/test/test_xml_etree.py

@@ -1436,17 +1436,39 @@ class IterparseTest(unittest.TestCase):
 
     def test_resource_warnings_not_exhausted(self):
         # Not exhausting the iterator still closes the underlying file (bpo-43292)
+        # Not closing before del should emit ResourceWarning
         it = ET.iterparse(SIMPLE_XMLFILE)
         with warnings_helper.check_no_resource_warning(self):
+            it.close()
             del it
             gc_collect()
 
+        it = ET.iterparse(SIMPLE_XMLFILE)
+        with self.assertWarns(ResourceWarning) as wm:
+            del it
+            gc_collect()
+        # Not 'unclosed file'.
+        self.assertIn('unclosed iterparse iterator', str(wm.warning))
+        self.assertIn(repr(SIMPLE_XMLFILE), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
+
         it = ET.iterparse(SIMPLE_XMLFILE)
         with warnings_helper.check_no_resource_warning(self):
+            action, elem = next(it)
+            it.close()
+            self.assertEqual((action, elem.tag), ('end', 'element'))
+            del it, elem
+            gc_collect()
+
+        it = ET.iterparse(SIMPLE_XMLFILE)
+        with self.assertWarns(ResourceWarning) as wm:
             action, elem = next(it)
             self.assertEqual((action, elem.tag), ('end', 'element'))
             del it, elem
             gc_collect()
+        self.assertIn('unclosed iterparse iterator', str(wm.warning))
+        self.assertIn(repr(SIMPLE_XMLFILE), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
 
     def test_resource_warnings_failed_iteration(self):
         self.addCleanup(os_helper.unlink, TESTFN)
@@ -1461,16 +1483,41 @@ class IterparseTest(unittest.TestCase):
                 next(it)
             self.assertEqual(str(cm.exception),
                     'junk after document element: line 1, column 12')
+            it.close()
             del cm, it
             gc_collect()
 
+        it = ET.iterparse(TESTFN)
+        action, elem = next(it)
+        self.assertEqual((action, elem.tag), ('end', 'document'))
+        with self.assertWarns(ResourceWarning) as wm:
+            with self.assertRaises(ET.ParseError) as cm:
+                next(it)
+            self.assertEqual(str(cm.exception),
+                    'junk after document element: line 1, column 12')
+            del cm, it
+            gc_collect()
+        self.assertIn('unclosed iterparse iterator', str(wm.warning))
+        self.assertIn(repr(TESTFN), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
+
     def test_resource_warnings_exhausted(self):
         it = ET.iterparse(SIMPLE_XMLFILE)
         with warnings_helper.check_no_resource_warning(self):
             list(it)
+            it.close()
             del it
             gc_collect()
 
+        it = ET.iterparse(SIMPLE_XMLFILE)
+        with self.assertWarns(ResourceWarning) as wm:
+            list(it)
+            del it
+            gc_collect()
+        self.assertIn('unclosed iterparse iterator', str(wm.warning))
+        self.assertIn(repr(SIMPLE_XMLFILE), str(wm.warning))
+        self.assertEqual(wm.filename, __file__)
+
     def test_close_not_exhausted(self):
         iterparse = ET.iterparse
 

Lib/xml/etree/ElementTree.py

@@ -1261,16 +1261,20 @@ def iterparse(source, events=None, parser=None):
     gen = iterator(source)
     class IterParseIterator(collections.abc.Iterator):
         __next__ = gen.__next__
+
         def close(self):
+            nonlocal close_source
             if close_source:
                 source.close()
+                close_source = False
             gen.close()
 
-        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 iterparse iterator {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.