[issue34941] xml.etree.ElementTree findall() fails when using custom TreeBuilder

[Jack Jansen]

New submission from Jack Jansen <jackjansen at users.sourceforge.net>:

When using a TreeBuilder with a custom factory (returning a subclass of Element with some extra functionality) there is an issue with findall().

XPaths using an indexed predicate no longer work: the findall() result is always empty. The attached test script shows the problem.

I have analysed this as far as finding that the issue is in ElementPath.prepare_predicate.<locals>.select(), the last one. Specifically, the statement
    elems = list(parent.findall(elem.tag))
always returns an empty list (if the Element class is subclassed).

When using Python 2.7 everything works fine. When adding a findall() method to the Element subclass that simply calls Element.findall() everything also works fine. I suspect some issue with the _elementtree C implementation but I don't understand it.

----------
components: Library (Lib)
files: testetns.py
messages: 327385
nosy: jackjansen
priority: normal
severity: normal
stage: needs patch
status: open
title: xml.etree.ElementTree findall() fails when using custom TreeBuilder
type: behavior
versions: Python 3.7
Added file: https://bugs.python.org/file47859/testetns.py

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34941>
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