ElementTree: Element.getiterator(tag) broken in 3.6

[mitya57]

BPO	28314
Nosy	@vstinner, @ned-deily, @serhiy-storchaka, @mitya57
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	etree.patch test_getiterator.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2016-10-25.07:38:56.161>
created_at = <Date 2016-09-29.19:44:06.336>
labels = ['3.7', 'library', 'type-crash']
title = 'ElementTree: Element.getiterator(tag) broken in 3.6'
updated_at = <Date 2017-03-31.16:36:26.838>
user = 'https://github.com/mitya57'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:26.838>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2016-10-25.07:38:56.161>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2016-09-29.19:44:06.336>
creator = 'mitya57'
dependencies = []
files = ['44881', '44882']
hgrepos = []
issue_num = 28314
keywords = ['patch']
message_count = 8.0
messages = ['277717', '277719', '277721', '277722', '277723', '277724', '277725', '279370']
nosy_count = 5.0
nosy_names = ['vstinner', 'ned.deily', 'python-dev', 'serhiy.storchaka', 'mitya57']
pr_nums = ['552']
priority = None
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue28314'
versions = ['Python 3.6', 'Python 3.7']

[mitya57]

The documentation says that getiterator() still accepts a tag argument, but it does not:

>>> from xml.etree.ElementTree import Element
>>> el = Element('foo')
>>> el.getiterator('bar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: ../Python/getargs.c:1508: bad argument to internal function
>>> el.getiterator(tag='bar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: iter() takes at most 1 argument (140172072006928 given)

This is with Python 3.6.0 beta 1 on Debian GNU/Linux amd64.

[ned-deily]

Even better:

Python 3.6.0b1 (v3.6.0b1:5b0ca4ed5e2f, Sep 12 2016, 09:24:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from xml.etree.ElementTree import Element
>>> el = Element('foo')
>>> el.getiterator('bar')
Segmentation fault: 11

[vstinner]

The bug seems related to the new FASTCALL calling convention introduced in Python 3.6b1. For an unknown reason, the METH_FASTCALL defined in Modules/clinic/_elementtree.c on _elementtree_Element_iter() seems to be ignored or lost somewhere?

[vstinner]

Oh... Modules/_elementtree.c uses a function defined in Modules/clinic/_elementtree.c. It hardcodes flags, whereas flags changed.

Maybe the alias should be created differently to avoid such issue in the future?

Moreover, obviously, we lack unit tests on this getiterator() method.

[python-dev]

New changeset 1e29dca5dc4c by Victor Stinner in branch '3.6':
Fix xml.etree.ElementTree.Element.getiterator()
https://hg.python.org/cpython/rev/1e29dca5dc4c

[vstinner]

I pushed the first obvious fix to unblock the 3.6 beta 2 release scheduled for next monday.

[serhiy-storchaka]

Here is a test.

[python-dev]

New changeset ca1b91829edf by Serhiy Storchaka in branch '3.5':
Issue bpo-28314: Added tests for xml.etree.ElementTree.Element.getiterator().
https://hg.python.org/cpython/rev/ca1b91829edf

New changeset c14a2d2a3b19 by Serhiy Storchaka in branch '3.6':
Issue bpo-28314: Added tests for xml.etree.ElementTree.Element.getiterator().
https://hg.python.org/cpython/rev/c14a2d2a3b19

New changeset 17334c1d9245 by Serhiy Storchaka in branch 'default':
Issue bpo-28314: Added tests for xml.etree.ElementTree.Element.getiterator().
https://hg.python.org/cpython/rev/17334c1d9245