What's the best start of cell marker for Python and Julia scripts?

[mwouts]

We're currently using # + {} as start of cell marker. But possibly # + (when not following a commented line) would be just enough. And also, Hydrogen seems to use # %%name of cell. Can we design a common, simple and clear pattern?

[grst]

maybe stick to hydrogen
-> one standard less and hydrogen is pretty established.

Would hydrogen blow up when adding metadata like this?

# %%name-of-cell {metadata}

[kylebarron]

That would be fine. Once Hydrogen sees ${comment symbol} %% it treats that line as the start of a block.

Source:
https://github.com/nteract/hydrogen/blob/58ba87e1747366c46f9baca87dcdda27401f6a5a/lib/code-manager.js#L138

[mwouts]

Sure! Yet,

• Jupytext has a very different practice of cells markers (few explicit markers, start+end) than Hydrogen (all cells are marked, start only). This is also discussed here. Hydrogen syntax is simpler to parse. Jupytext's cells are more difficult to parse, but arbitrary python files can be converted to notebooks, and converted back to the original python files without loss or additional markers.
• The definition of markdown cells in Hydrogen is pending (Export Notebook - markdown cells not correctly exported to ipynb nteract/hydrogen#1296, Support export markdown cell when export file as Jupyter Notebook nteract/hydrogen#1183)

For now I would be in favor of

• preserving the current 'plain python' format for Jupytext's python scripts, and simplify # + {} to # + for explicit code cells with no metadata
• implementing a 'hydrogen script' format (R, Julia, Python) in Jupytext when specifications for markdown cells (and cell metadata) are chosen. The Hydrogen format must remain easy to parse (simply split on cell markers), as an additional JavaScript parser will have to be implemented in Atom.

[mwouts]

I've found more python scripts with cells defined with #%%! VS code has a plugin that uses that convention. It's also used by Spyder. No sign of markdown cells yet, though.

[mwouts]

I'll work on an Hydrogen/VS code/Spyder compatible format at #59 (see there for possible specifications of the format). With this issue I'll just simplify # + {} into the lighter # + when possible.