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[3.13] gh-142145: Remove quadratic behavior in node ID cache clearing (GH-142146) #142210

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[3.13] gh-142145: Remove quadratic behavior in node ID cache clearing (GH-142146) #142210

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18 changes: 18 additions & 0 deletions Lib/test/test_minidom.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

import copy
import pickle
import time
import io
from test import support
import unittest
Expand Down Expand Up @@ -173,6 +174,23 @@ def testAppendChild(self):
self.assertEqual(dom.documentElement.childNodes[-1].data, "Hello")
dom.unlink()

def testAppendChildNoQuadraticComplexity(self):
impl = getDOMImplementation()

newdoc = impl.createDocument(None, "some_tag", None)
top_element = newdoc.documentElement
children = [newdoc.createElement(f"child-{i}") for i in range(1, 2 ** 15 + 1)]
element = top_element

start = time.time()
for child in children:
element.appendChild(child)
element = child
end = time.time()

# This example used to take at least 30 seconds.
self.assertLess(end - start, 1)
Comment on lines +191 to +192
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@hugovk hugovk Dec 5, 2025 •
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The three failures we've had:

AssertionError: 1.8501551151275635 not less than 1
AssertionError: 2.0126874446868896 not less than 1
AssertionError: 2.0126874446868896 not less than 1

All are much less than the commented "at least 30 seconds".

Shall we use something like 2.1 or 2.5 or 3 in this test?

Suggested change
# This example used to take at least 30 seconds.
self.assertLess(end - start, 1)
# This example used to take at least 30 seconds.
self.assertLess(end - start, 3)

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@Yhg1s Yhg1s Dec 5, 2025

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3 isn't enough to make it non flaky on slow or loaded systems, or when small shifts in time happen. Frankly, this is always going to flaky, no matter the limit, because it's using time.time(). I think this is a bad idea to include in tests.

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@Yhg1s Yhg1s Dec 5, 2025

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I suggest we get this in with a check for 10 or 20 seconds just to get the release unblocked and not creating an overly flaky test, and continue discussion on how this could be reliably tested on main.


def testAppendChildFragment(self):
dom, orig, c1, c2, c3, frag = self._create_fragment_test_nodes()
dom.documentElement.appendChild(frag)
Expand Down
9 changes: 1 addition & 8 deletions Lib/xml/dom/minidom.py
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Original file line number Diff line number Diff line change
Expand Up @@ -292,13 +292,6 @@ def _append_child(self, node):
childNodes.append(node)
node.parentNode = self

def _in_document(node):
# return True iff node is part of a document tree
while node is not None:
if node.nodeType == Node.DOCUMENT_NODE:
return True
node = node.parentNode
return False

def _write_data(writer, text, attr):
"Writes datachars to writer."
Expand Down Expand Up @@ -1555,7 +1548,7 @@ def _clear_id_cache(node):
if node.nodeType == Node.DOCUMENT_NODE:
node._id_cache.clear()
node._id_search_stack = None
elif _in_document(node):
elif node.ownerDocument:
node.ownerDocument._id_cache.clear()
node.ownerDocument._id_search_stack= None

Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Remove quadratic behavior in ``xml.minidom`` node ID cache clearing.
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