Add function alphanumeric_key in __all__ of io.collection.py

[sciunto]

Description

Fixes #4309

Test:

In [3]: skimage.lookfor('alphanu' 
   ...: )                                                                                                                                                                                                                                    
Search results for 'alphanu'
----------------------------
skimage.io.alphanumeric_key
    Convert string to list of strings and ints that gives intuitive sorting.
skimage.io.ImageCollection
    Load and manage a collection of image files.

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.
• Consider backporting the PR with @meeseeksdev backport to v0.14.x

[soupault]

Frankly speaking, I am not sure if this is a good addition to the public API, since the function is rather simple and covers only quite specific naming case. Perhaps, we could have more core members to share their opinions.

[jni]

well, we wanted to use it in at least one other place, namely napari. I also don't think it warrants its own package or anything (hello left-pad), and it is complex enough that I don't want to reimplement it everywhere... But I agree that it's kinda weird to provide it. I just don't think there is a better option.

[hmaarrfk]

https://pypi.org/project/natsort/ ???

[jni]

@hmaarrfk that's pretty nice, thanks!

[sciunto]

Should I close this? Should we remove this function?

[jni]

I would not remove it for sure — no chance we want that dependency. The only question is whether we want it to be part of the public API. Of that I’m not sure. I suggest we wait for more devs to weigh in.

[sciunto]

I would be in favor to add the link to natsort in the dosctring as an indication.

[stefanv]

Err, woops, just left a comment on the wrong issue. Let's try again :)

@jni I'd suggest renaming this function to better explain what it does, as well as moving it from io to util.

[lagru]

How about as_alphanumeric_key or as_natural_sort_key? I like the latter.

[emmanuelle]

This one is a bit tricky, maybe we should take the opportunity of a dev meeting to discuss the best name.

[emmanuelle]

As discussed in the Atlantic meeting Jan 31st, let's keep this function private and add an example with natsort in the documentation.

[jni]

Cool, sounds good to me.