Error if kernelspec missing

[psychemedia]

I've been experimenting with various publishing workflows, one of which involves creating .md and then converting it to .ipynb with Jupytext.

Atm, Jupytext doesn't seem to create a kernelspec element in the notebook format (it is created if the notebook is opened and saved) which causes an error when running Jupyter Book on .ipynb created straight from .md using Jupytext:

Traceback (most recent call last):
  File "/usr/local/bin/jupyter-book", line 10, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.7/site-packages/jupyter_book/main.py", line 29, in main
    commands[args.command]()
  File "/usr/local/lib/python3.7/site-packages/jupyter_book/commands/build.py", line 52, in build
    PATH_TEMPLATE, local_build, execute, overwrite)
  File "/usr/local/lib/python3.7/site-packages/jupyter_book/build.py", line 221, in build_book
    kernel_name = data['metadata']['kernelspec']['name']
KeyError: 'kernelspec'

[joergbrech]

You are right, I think we should make sure that the kernelspec element (and the metadata element) exist before we try to read them, see the corresponding PR.

[psychemedia]

@joergbrech Great, thanks..

There was also a workaround from the Jupytext side.