`XMLParser.__init__()` leaking refs when called twice

[maurycy]

Bug report

Bug description:

Similarly to gh-147998, found with @devdanzin's Claude Code toolkit.

The XMLParser constructor does not care about already created objects if called twice:

cpython/Modules/_elementtree.c

Line 3716 in dea4083

self->entity = PyDict_New();

cpython/Modules/_elementtree.c

Line 3720 in dea4083

self->names = PyDict_New();

cpython/Modules/_elementtree.c

Line 3726 in dea4083

self->parser = EXPAT(st, ParserCreate_MM)(encoding, &ExpatMemoryHandler, "}");

etc.

I think it exists since 52467b1

Reproduction

2026-04-03T21:46:41.206031691+0000 maurycy@weiss /home/maurycy/cpython (main) % cat 1.py 
import gc
import xml.etree.ElementTree as ET


for i in range(20_000):
    p = ET.XMLParser()
    del p
    if i % 1000 == 0:
        gc.collect()
2026-04-03T21:46:41.431691265+0000 maurycy@weiss /home/maurycy/cpython (main) % cat 2.py
import gc
import xml.etree.ElementTree as ET


for i in range(20_000):
    p = ET.XMLParser()
    p.__init__()
    del p
    if i % 1000 == 0:
        gc.collect()

Then:

2026-04-03T21:50:56.840438090+0000 maurycy@weiss /home/maurycy/cpython (main) % ./python.exe -X showrefcount 1.py                                    
[0 refs, 0 blocks]
2026-04-03T21:51:01.610978599+0000 maurycy@weiss /home/maurycy/cpython (main) % ./python.exe -X showrefcount 2.py 
[343430 refs, 302265 blocks]

CPython versions tested on:

CPython main branch

Operating systems tested on:

% cat /etc/debian_version 
13.4

Linked PRs

• gh-148058: Do not refleak when XMLParser.__init__() called many times #148061

[ZeroIntensity]

Is there any precedent for fixing issues like this? In the past, we've rejected bug reports involving calling __init__ on the same object multiple times because fixing it generally slows down code, and nobody does it in practice.

[maurycy]

@ZeroIntensity

• super.__init__ leaks memory if called multiple times #70905 (comment)
• various refleaks when calling the __init__() method of an object more than once #75968
• Bug: Reference leak in _asyncio_Task___init___impl in _asynciomodule.c #126083