Document various options for getting the absolute path from pathlib.Path objects

[brettcannon]

BPO	39090
Nosy	@brettcannon, @pfmoore, @eryksun, @vedgar, @PythonCHB, @designerzim, @florisla, @barneygale, @John-Hennig

^{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 2019-12-18.18:20:50.641>
labels = ['type-feature', '3.9', 'docs']
title = 'Document various options for getting the absolute path from pathlib.Path objects'
updated_at = <Date 2022-04-04.13:40:35.399>
user = 'https://github.com/brettcannon'

bugs.python.org fields:

activity = <Date 2022-04-04.13:40:35.399>
actor = 'barneygale'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-12-18.18:20:50.641>
creator = 'brett.cannon'
dependencies = []
files = []
hgrepos = []
issue_num = 39090
keywords = []
message_count = 15.0
messages = ['358638', '358854', '361698', '361877', '361878', '361885', '362030', '362578', '362579', '362627', '387634', '416465', '416470', '416488', '416668']
nosy_count = 11.0
nosy_names = ['brett.cannon', 'paul.moore', 'docs@python', 'eryksun', 'veky', 'ChrisBarker', 'Zim', '4-launchpad-kalvdans-no-ip-org', 'florisla', 'barneygale', 'John-Hennig']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39090'
versions = ['Python 3.9']

[brettcannon]

The question on how best to get an absolute path from a pathlib.Path object keeps coming up (see https://bugs.python.org/issue29688, https://discuss.python.org/t/add-absolute-name-to-pathlib-path/2882/, and https://discuss.python.org/t/pathlib-absolute-vs-resolve/2573 as examples).

As pointed out across those posts, getting the absolute path is surprisingly subtle and varied depending on your needs. As such we should probably add a section somewhere in the pathlib docs explaining the various ways and why you would choose one over the other.

[PythonCHB]

Yes Please!

I'd offer to help, but I really don't get the intricacies involved. I will offer to proofread and copy-edit though, if that's helpful.

And I note that coincidentally, just in the last week, I needed to make an absolute path from a Path, and it took me far too long to figure out that .resolve() would do it for me. Then I needed to do it again three days later, and it again took a while -- "resolve" is simply not mnemonic for me, and I'm guessing a lot of people have the same issue.

And I didn't find .absolute(), cause it's not documented. I see in issue bpo-29688 that there are reasons for that, but I'll make a plea:

Please document .absolute(), even if those docs say something like "may not work in all circumstances, not well tested". Alternatively, if it's decided that folks should just use .resolve() in all cases anyway, then make .absolute() an alias for .resolve().

Or if that's not a good option, then at least put some prominent notes in resolve() so people will find it.

Also -- I needed to read the resolve() docs carefully (and then test) to see if it was what I wanted - which I know, is what this issue is about.

In short -- I understand that this is a complex issue, but making an absolute path is a pretty common use case, and we've had os.path.abspath() for decades, so there should be one obvious way to do it, and it should be easily discoverable.

NOTE: even if there is no one to do the work of properly testing .absolute() at this point, it would b nice to at least decide now what the long term goal is -- will there be an absolute() or is resolve() all we really need?

[pfmoore]

In short -- I understand that this is a complex issue, but making an absolute path is a pretty common use case, and we've had os.path.abspath() for decades, so there should be one obvious way to do it, and it should be easily discoverable.

+1 on this.

Given that (as far as I can tell from the various discussions) resolve works fine as long as the file exists, maybe the key distinction to make is whether you have an existing file or not.

(More subtle questions like UNC path vs drive letter, mentioned on the Discourse thread, are probably things that we can defer to a "more advanced cases" discussion in the docs).

[florisla]

I've written an "Absolute paths" section based on the knowledge I found in the various threads.

Any review is appreciated.

https://github.com/florisla/cpython/tree/pathlib-chapter-absolute-paths

With some related documentation changes:

https://github.com/florisla/cpython/tree/absolute-path-related-improvements

[pfmoore]

You've provided links to your branches, but not to the specific text you're proposing to add. Can you link to a diff or something that shows what you've added more precisely?

[florisla]

This is the new chapter:

florisla@c146ad3

[vedgar]

If we want something mnemonic, I'm sure nothing beats __abs__. (Hey, we have __truediv__ already!;)

[florisla]

@chrisbarker,

Could you review the proposed addition to the documentation?

florisla@c146ad3

[florisla]

(sorry, didn't see the GitHub comments before... I'll process those first.)