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gh-101438: Avoid reference cycle in ElementTree.iterparse. #114269

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Merged
merged 5 commits into from
Jan 23, 2024
Merged

gh-101438: Avoid reference cycle in ElementTree.iterparse. #114269

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2119f17
gh-101438: Avoid reference cycle in ElementTree.iterparse.
colesbury Jan 18, 2024
8fabc7c
Avoid regression in bm_xml_etree performance.
colesbury Jan 19, 2024
1ae917e
Minor simplification
colesbury Jan 19, 2024
05baaad
Update Lib/xml/etree/ElementTree.py
colesbury Jan 23, 2024
307b375
Update 2024-01-18-22-29-28.gh-issue-101438.1-uUi_.rst
serhiy-storchaka Jan 23, 2024
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27 changes: 17 additions & 10 deletions Lib/xml/etree/ElementTree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@
import collections
import collections.abc
import contextlib
import weakref

from . import ElementPath

Expand Down Expand Up @@ -1223,13 +1224,14 @@ def iterparse(source, events=None, parser=None):
# parser argument of iterparse is removed, this can be killed.
pullparser = XMLPullParser(events=events, _parser=parser)

def iterator(source):
if not hasattr(source, "read"):
source = open(source, "rb")
close_source = True
else:
close_source = False

def iterator(source):
try:
if not hasattr(source, "read"):
source = open(source, "rb")
close_source = True
yield None
while True:
yield from pullparser.read_events()
# load event buffer
Expand All @@ -1239,18 +1241,23 @@ def iterator(source):
pullparser.feed(data)
root = pullparser._close_and_return_root()
yield from pullparser.read_events()
it.root = root
it = wr()
if it is not None:
it.root = root
finally:
if close_source:
source.close()

class IterParseIterator(collections.abc.Iterator):
__next__ = iterator(source).__next__
it = IterParseIterator()
it.root = None
del iterator, IterParseIterator

next(it)
def __del__(self):
if close_source:
source.close()

it = IterParseIterator()
wr = weakref.ref(it)
del IterParseIterator
Comment on lines +1258 to +1260
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I am curious, why previously both iterator and IterParseIterator names were deleted, but now only IterParseIterator? And what is the purpose of this statement in the first place? I was thinking that iterator.__closure__ stores references to these objects; therefore, unnecessary references should be deleted. However, as per my checks, closure stores only referenced variables inside; pullparser, close_source and wr in this case.

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I also noticed that it.root = None was deleted. This fact is not documented, but this may still cause unintended errors on the user side if they use root.

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I think you are right about the it.root = None. I did not intend a behavioral change here, so it seems like a good idea to add it back.

I don't think the del statements matter one way or the other. They look like they break a cycle, but not really, but they also are harmless.

return it


Expand Down
4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Library/2024-01-18-22-29-28.gh-issue-101438.1-uUi_.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Avoid reference cycle in ElementTree.iterparse. The iterator returned by
``ElementTree.iterparse`` may hold on to a file descriptor. The reference
cycle prevented prompt clean-up of the file descriptor if the returned
iterator was not exhausted.