Provide list.rindex()

[johnlinp]

BPO	36639
Nosy	@rhettinger, @vstinner, @serhiy-storchaka, @johnlinp, @tirkarthi
PRs	bpo-36639: Provide list.rindex() #12851

^{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 2019-04-17.08:38:40.936>
created_at = <Date 2019-04-16.06:46:24.224>
labels = ['interpreter-core', 'type-feature', '3.9']
title = 'Provide list.rindex()'
updated_at = <Date 2019-04-24.08:32:51.896>
user = 'https://github.com/johnlinp'

bugs.python.org fields:

activity = <Date 2019-04-24.08:32:51.896>
actor = 'johnlinp'
assignee = 'none'
closed = True
closed_date = <Date 2019-04-17.08:38:40.936>
closer = 'rhettinger'
components = ['Interpreter Core']
creation = <Date 2019-04-16.06:46:24.224>
creator = 'johnlinp'
dependencies = []
files = []
hgrepos = []
issue_num = 36639
keywords = ['patch']
message_count = 9.0
messages = ['340312', '340314', '340317', '340319', '340383', '340417', '340751', '340758', '340762']
nosy_count = 6.0
nosy_names = ['rhettinger', 'vstinner', 'SilentGhost', 'serhiy.storchaka', 'johnlinp', 'xtreak']
pr_nums = ['12851']
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36639'
versions = ['Python 3.9']

[johnlinp]

There are str.index() and str.rindex(), but there is only list.index() and no list.rindex(). It will be very handy if we provide it.

[SilentGhost]

That's a fairly bare-bones implementation you're providing in your PR. Such a feature would need documentation, tests, news entry. I'm not endorsing or discarding your idea, but these are the general requirements for the feature of this level.

[tirkarthi]

New methods to builtins generally require a python-ideas discussion. Search brings up an old discussion for rindex and rremove : https://mail.python.org/pipermail/python-ideas/2009-May/004506.html . It also would make users ask for tuple.rindex as in the linked discussion.

[johnlinp]

Hi @SilentGhost, Thank you for the feedback. The PR is only a WIP and a placeholder.

Hi @XTreak, Thank you for searching that mailing list for me. However, after reading the thread, it seems that we didn't have any conclusion on whether we should add list.rindex() or not. Did I miss something?

[rhettinger]

There were known, strong use cases for str.rindex(). The list.rindex() method was intentionally omitted. AFAICT no compelling use cases have arisen, so we should continue to leave it out. In general, we don't grow the core APIs unnecessarily.

Thank you for the suggestion, but we should pass on this unless actual, real-world use cases arise often enough to warrant its inclusion.

[johnlinp]

Hi @rhettinger ,

Thank you for the reply. May I ask what is the known, strong use cases for str.rindex()?

[johnlinp]

From the discussion in https://mail.python.org/pipermail/python-ideas/2019-April/056416.html, Guido said:

Some use cases for rindex() on strings that I found in a large codebase
here include searching a pathname for the final slash, a list of
comma-separated items for the last comma, a fully-qualified module name for
the last period, and some ad-hoc parsing of other things. The "last
separator" use cases are the most common and here rindex() sounds very
useful.

I guess that's strong enough.

[SilentGhost]

I guess that's strong enough.

As a str.rindex use case. I don't read it as Guido's endorsing list.rindex proposal, johnlinp.

[johnlinp]

Hi @SilentGhost,

Yes, sorry I didn't make it clear. I was just posting the discussion here for some reference, not claiming that this issue should be reopened.