Add support for Python cells

[jonatanklosko]

This introduces support for evaluating Python code. Once Python is enabled, an extra setup cell appears, where the user can specify the Python version and any packages they need, using the pyproject.toml format. Python cells are interoperable with Elixir cells (in terms of variables), similarly to the Erlang cells we already have.

This works on top of pythonx. In fact, we could make it work as smart cells, however making it first class provides a more consistent experience (e.g. switching cell language, having pyproject.toml in the setup section) and will allow us to implement features beyond the scope of smart cells (e.g. intellisense).

pythoncells.mp4

After these changes, there are a few things I want to revisit regarding code structure, but that can come later, and this PR is already big.

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[georgeguimaraes]

Wow, this makes me very happy! :)

[josevalim]

Where did we land on the discussion between using the application environment for the install vs an explicit call to uv_init? If we could simply add it as a dep, it would be better, but I don't recall the details. :)

[josevalim]

Oh, I think we had to do it after the fact, hence why we pretend this to be its own cell. 👍

[jonatanklosko]

For me the main reason is that to use app config, we would need to change the setup cell code that gets evaluated, and I think that's too much. We should evaluate exactly what the user sees, otherwise errors could be confusing.

We also considered putting the config before the setup cell, but then the config is not a part of Mix.install cache, which is a problem.

Doing it separately also means it's cached separately from Mix.install, which is good. The only drawback is that the installation does not end up in priv, but we said we can add extra copy paths to FLAME later.

[josevalim]

It is worth keeping in mind that this sends duplicates SVG for each cell. I wonder if instead we should move this to CSS and how we approach other icons?

[josevalim]

This is fantastic! 🤩

My only comment is about the UI of the setup cell, I was thinking by having two distinct cells, which are collapsed independently. The addition of Python would work as any other cell, by mousing over:

[ Elixir dependencies and setup                              🟢 ]
                              [ + Python ]

And then, after configured:

[ Elixir dependencies and setup                              🟢 ]
[ Python dependencies and setup                              🟢 ]

WDYT?

[jonatanklosko]

My only comment is about the UI of the setup cell, I was thinking by having two distinct cells, which are collapsed independently.

Those are totally separate cells. When I added the cell initially, they were collapsed separately, but to me it felt weird to see only part of the setup at once (and two collapsed items are more noise). One other factor is the "Setup" evaluation button, which I think we should have only one and it effectively evaluates the whole setup section. If any of the setup fails, the runtime need to be restarted to try again. So my idea was to have separate cells, but make the "setup" feel more like a single entity. WDYT?

[josevalim]

So my idea was to have separate cells, but make the "setup" feel more like a single entity.

What you said makes sense. My only complaint then is that "+ Python" and "↳ Python" feels different. For the plug "+ Python", I guess we could use the regular "+ Python" button that we use to add new cells, perhaps make it always visible. But I am unsure what to do about the "↳ Python". Part of me says it could be removed but given the cell indicator says TOML, I am not sure. In other words, it would be nice if they felt more consistent.

[jonatanklosko]

But I am unsure what to do about the "↳ Python"

That was my attempt at conveying the cell is like an extra setup on top of the main Elixir one. But I can totally be something else. For example:

(not sure about the last one, saying pyproject.toml is kinda weird, but just giving ideas)

[jonatanklosko]

I guess we could use the regular "+ Python" button that we use to add new cells, perhaps make it always visible.

I started with the regular button, but if the idea is to always show it below the setup cell, then it felt like too much, so I went with a more subtle one. It can also be slightly confusing to use the same + Python buton in two places and it does something very different.

[josevalim]

Thanks to @cocoa-xu and @cigrainger for the ideas, suggestions, and getting this party started!