Add concat functionality to ElementTree xpath find

[jjolly]

BPO	32476
Nosy	@scoder, @ned-deily, @matrixise, @jjolly
PRs	bpo-32476 : Add concat function for ElementTree find #5251
Files	etree-concat.patch: Patch to add concat functionality to predicates in etree

^{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 = None
created_at = <Date 2018-01-01.19:19:06.794>
labels = ['expert-XML', 'type-feature', 'library', '3.9']
title = 'Add concat functionality to ElementTree xpath find'
updated_at = <Date 2020-04-12.13:29:36.039>
user = 'https://github.com/jjolly'

bugs.python.org fields:

activity = <Date 2020-04-12.13:29:36.039>
actor = 'scoder'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'XML']
creation = <Date 2018-01-01.19:19:06.794>
creator = 'jjolly'
dependencies = []
files = ['47360']
hgrepos = []
issue_num = 32476
keywords = ['patch']
message_count = 7.0
messages = ['309344', '311259', '311273', '311277', '311399', '313959', '366247']
nosy_count = 5.0
nosy_names = ['scoder', 'ned.deily', 'eli.bendersky', 'matrixise', 'jjolly']
pr_nums = ['5251']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32476'
versions = ['Python 3.9']

[jjolly]

The current implementation of the xpath specification in ElementTree does not allow for predicates that may contain both an apostrophe and a quote. Either one or the other is allowed, but escaping (either string escaping using the backslash or html escaping) is not supported.

A simple solution would be to implement the xpath concat function for predicates. This would allow the combination of quote types in the predicate. Attached is a proposed patch for this fix.

[matrixise]

as explained on the PR, maybe you could add in the documentation.

..versionadded:: 3.7
Support of the XPath concat function

but maybe your PR is too late because 3.7 starts to be in the frozen period for the features.

[jjolly]

I understand that the feature is likely too late, but I do not want it to get lost. Is there any way to make certain this feature is accepted for the next release? Do I just select the 3.8 version for this issue?

[matrixise]

I think (but not sure) that your feature will be included in 3.8 because 3.7 has been frozen today :/

@ned do you think you could integrate this functionality in 3.7 or 3.8 ?

[ned-deily]

Sorry, I think this qualifies as a new feature and thus needs to go in 3.8. Plus it should get a wider review from those with ET experience. Perhaps @scoder would be willing go take a look.

[scoder]

I can't see why this should be restricted to attribute values and not text content in general. Therefore, I would suggest adding general support for functions, and making this only a special case. Otherwise, this would only solve a very niche problem, and would require pretty much a rewrite in order to extend it into the "obvious" direction.

[scoder]

I think the use case of quote escaping is too niche for a feature like concat(), where I (at least) would expect to be able to dynamically concatenate text content, not just constant strings.

There seem to be at least a few alternatives to the usage of concat():

https://stackoverflow.com/questions/12403870/how-to-escape-single-quote-in-xslt-substring-function

https://sqa.stackexchange.com/questions/26341/how-to-write-xpath-if-i-have-apostrophe-in-my-xpath-element

I think we should either implement concat() completely, or provide a different way to solve the concrete problem at hand.