Exporting cell-metadata with "@" or "/" in their names in md:myst format

[nthiery]

Description and use case

jupyterlab-slideshow (ex jupyterlab-deck) has a feature to configure the position of fragments in the page. These are configured using jupyterlab-fonts, in a cell metadata named @deathbeds/jupyterlab-fonts. Upon saving the file to md:myst, a warning is emitted:

UserWarning: The following metadata cannot be exported to the text notebook: ['@deathbeds/jupyterlab-fonts']

and indeed, that cell metadata is not exported. This prevents using this slideshow feature with md:myst notebooks.

And indeed, "/" and "@" are not accepted by jupytext as authorized characters in metadata keys:

jupytext/src/jupytext/cell_metadata.py

Line 62 in d3f9e77

_IS_VALID_METADATA_KEY = re.compile(r"^[a-zA-Z0-9_\.-]+$")

Is there a specific reason for excluding these characters? I have added them locally and so far everything is going smoothly.

I could provide a PR. To not do it on a character by character basis, is there some standard that we want to adhere to that would specify which characters should be accepted?

[mwouts]

Hi @nthiery , thank you for reaching out! From the comment above that variable I would say that the pattern was designed to match the metadata keys that I encountered in R Markdown notebooks. Of course we can consider extending it. I am open to a PR - it would be interesting to see if we have any tests on what is a valid metadata key... Thanks!

[nthiery]

Just to make sure it would not get drowned in my todo list, I made a crude PR #1445 with what worked for me.
If that's ok with you, it can be merged for now until we have something more systematic.

[mwouts]

Thanks @nthiery . I was wondering if you could add a very short example notebook under https://github.com/mwouts/jupytext/tree/main/tests/data/notebooks/inputs/ipynb_py ? It can be very short, I would just need one cell with the cell metadata that you mentioned above, this way we make sure that the new pattern works for all the export formats. Thanks!

[mwouts]

Hi @nthiery , I am planning to release v1.18.0 this weekend. Would you have a chance to share a short example notebook? No problem if a test fails, I can help with that - I just prefer to be sure beforehand. Thanks!

[nthiery]

Dear @mwouts,

Sorry for the late answer. Please find below a short example of slideshow using cell metadata with @... keys for configuring the spacial layout of slides. To view the slideshow, you can use the jupyterlab-slideshow pip package, and click on the orange icon in the toolbar.

jupytext-1441.md

[mwouts]

Thanks @nthiery for the example! I'll add it to the test notebook collection