Is it possible to distribute python filters?

[acederberg]

Description

Hi!

I could probably test this quickly but I think it is a worthwhile discussion. I looked and I didn't see any discussion about this directly so I decided I'd ask.

Is it possible to distribute filters in a language other than lua.
Of course, I assume adding additional dependencies might require more work out of the user (in my case s3cmd and panflute would be required by python) and it should not be a feature quarto to handle the deps. However, it would be good enough to specify the deps in a file included by the extension (e.g. just include requirements.txt with the extension, in the case of python).

I see in distributing a lua file is not necessarily required so I am wondering if I could do something like

title: My Filter
author: Cooltools
version: 1.0.0
quarto-required: ">=1.2.0"
contributes:
  filters:
    - my-filter.py

for a python filter.

[mcanouil]

Did you look at Pandoc filters documentation? https://pandoc.org/filters.html
That's what is used in Quarto.

Quarto extension is an additional layer which might not support everything.
At least, you could try directly in a document:

filters:
  - my-filter.py

[acederberg]

Did you look at Pandoc filters documentation? https://pandoc.org/filters.html

Yes I have read the pandoc docs and have implemented exactly this in a single document. So certainly adding filters in the yaml front matter of an individual document does work.

I think filter was a poor choice of phrasing on my part - I mean can I distribute an extension containing a filter that is a python file and have it be installable with quarto add? I have a number of filters that I have written locally that I might eventually distribute.

[mcanouil]

I guess, the best way to know is to try it out, but if it works already in filters, it's likely going to work in extensions.

[acederberg]

That is great to hear. I'll share my results when/if it happens. Thank you for your help.

[mcanouil]

If it does, we might want to add a note that filters are not limited to Lua.

[athyfr]

From my experiments, it seems that Python filters do not currently work through the YAML frontmatter. My guess is that it's just an oversight in the Quarto source code, as Pandoc python filters do exist…

[mcanouil]

@athyfr I tried this with the current development version and couldn't reproduce it. A Python filter works for me both from the front matter and from an extension that lists it under contributes.filters.

The only way I could make it fail was to leave out a python command on the PATH. Pandoc runs a .py filter with python, not python3, unless the file is executable. In that case you get Could not find executable python.

Could you share a few details so I can look into it?

• Your Quarto version, from quarto --version, and your operating system.
• A minimal .qmd and filter that show the problem.
• The full error message you get when rendering.
• The output of which python and which python3, or where python on Windows.

[athyfr]

Oh, lol, oops. Forgot to install Python in a devenv environment, as I usually do. Works now!