Support cell.source as [list, of, strings]

[Wh1isper]

Description

https://nbformat.readthedocs.io/en/latest/format_description.html#cell-types

There are a few basic cell types for encapsulating code and text. All cells have the following basic structure:

{ "cell_type" : "type", "metadata" : {}, "source" : "single string or [list, of, strings]", }

In Jupyterlab3.x, cell.source is [list, of, strings], which causes

  File "/opt/conda/lib/python3.9/site-packages/jupyter_ydoc/ydoc.py", line 30, in source
    return self.set(value)
  File "/opt/conda/lib/python3.9/site-packages/jupyter_ydoc/ydoc.py", line 197, in set
    self._ycells.extend(t, [self.create_ycell(cell) for cell in cells])
  File "/opt/conda/lib/python3.9/site-packages/jupyter_ydoc/ydoc.py", line 197, in <listcomp>
    self._ycells.extend(t, [self.create_ycell(cell) for cell in cells])
  File "/opt/conda/lib/python3.9/site-packages/jupyter_ydoc/ydoc.py", line 127, in create_ycell
    cell["source"] = Y.YText(cell["source"])
TypeError: argument 'init': 'list' object cannot be converted to 'PyString'

Reproduce

example ipynb json:

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "4c8d2523-c9e8-4102-8949-8ec23e2be509",
   "metadata": {},
   "outputs": [],
   "source": [
    "print('hello world')"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3 (ipykernel)",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.9.12"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 5
}

Expected behavior

Context

• Operating System and version:
• Browser and version:
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[Wh1isper]

I opened a pr for this: https://github.com/jupyter-server/jupyter_ydoc/pull/112

[Wh1isper]

fixed: https://github.com/jupyter-server/jupyter_ydoc/pull/112