Document and test finalizer modifying the list

Author: vstinner

Doc/c-api/list.rst

@@ -59,6 +59,12 @@ List Objects
    Raise an exception and return ``-1`` if *list* is not a :class:`list`
    object.  Return 0 on success.
 
+   .. note::
+
+      If a finalizer (:meth:`object.__del__`) of a deleted item modify the
+      list, it is possible that the list is not empty after calling this
+      function.
+
    .. versionadded:: 3.13
 
 
@@ -149,6 +155,12 @@ List Objects
    Return ``0`` on success, ``-1`` on failure.  Indexing from the end of the
    list is not supported.
 
+   .. note::
+
+      If *itemlist* is ``NULL`` to delete items and a finalizer
+      (:meth:`object.__del__`) of a deleted item modify the list, it is
+      possible that the list is longer than expected.
+
 
 .. c:function:: int PyList_Sort(PyObject *list)
 

Lib/test/test_capi/test_list.py

@@ -1,5 +1,6 @@
+import gc
+import weakref
 import unittest
-import sys
 from test.support import import_helper
 from collections import UserList
 _testcapi = import_helper.import_module('_testcapi')
@@ -12,6 +13,15 @@ class ListSubclass(list):
     pass
 
 
+class DelAppend:
+    def __init__(self, lst, item):
+        self.lst = lst
+        self.item = item
+
+    def __del__(self):
+        self.lst.append(self.item)
+
+
 class CAPITest(unittest.TestCase):
     def test_check(self):
         # Test PyList_Check()
@@ -196,10 +206,10 @@ def test_list_getslice(self):
 
     def test_list_setslice(self):
         # Test PyList_SetSlice()
-        setslice = _testcapi.list_setslice
+        list_setslice = _testcapi.list_setslice
         def set_slice(lst, low, high, value):
             lst = lst.copy()
-            self.assertEqual(setslice(lst, low, high, value), 0)
+            self.assertEqual(list_setslice(lst, low, high, value), 0)
             return lst
 
         # insert items
@@ -231,8 +241,21 @@ def set_slice(lst, low, high, value):
         self.assertEqual(set_slice(lst, 0, len(lst), NULL), [])
         self.assertEqual(set_slice(lst, 3, len(lst), NULL), list("abc"))
 
-        self.assertRaises(SystemError, setslice, (), 0, 0, [])
-        self.assertRaises(SystemError, setslice, 42, 0, 0, [])
+        self.assertRaises(SystemError, list_setslice, (), 0, 0, [])
+        self.assertRaises(SystemError, list_setslice, 42, 0, 0, [])
+
+        # Item finalizer modify the list (clear the list)
+        lst = []
+        lst.append(DelAppend(lst, 'zombie'))
+        self.assertEqual(list_setslice(lst, 0, len(lst), NULL), 0)
+        self.assertEqual(lst, ['zombie'])
+
+        # Item finalizer modify the list (remove an list item)
+        lst = []
+        lst.append(DelAppend(lst, 'zombie'))
+        lst.extend("abc")
+        self.assertEqual(list_setslice(lst, 0, 1, NULL), 0)
+        self.assertEqual(lst, ['a', 'b', 'c', 'zombie'])
 
         # CRASHES setslice(NULL, 0, 0, [])
 
@@ -291,6 +314,12 @@ def test_list_clear(self):
         self.assertRaises(TypeError, list_clear, ())
         self.assertRaises(TypeError, list_clear, object())
 
+        # Item finalizer modify the list
+        lst = []
+        lst.append(DelAppend(lst, 'zombie'))
+        list_clear(lst)
+        self.assertEqual(lst, ['zombie'])
+
         # CRASHES list_clear(NULL)
 
     def test_list_extend(self):