jupytext gives incorrect warning "You have passed a file name to the '--to' option"

[jli]

I want to configure jupytext to save companion .py files for all .ipynb notebooks. I want the .py files to have a specific suffix, so that it's easy to identify those files.

This command works: jupytext --from ipynb --to __sidecar.py:percent <notebook file>
However, I get the following warning from jupytext:

[warning] You have passed a file name to the '--to' option, when a format description was expected. Maybe you want to use the '-o' option instead?

I'm guessing it's this code:

jupytext/jupytext/cli.py

Lines 463 to 466 in 57d83aa

	warnings.warn(
	"You have passed a file name to the '--to' option, "
	"when a format description was expected. Maybe you want to use the '-o' option instead?"
	)

And I'm guessing the issue is that the check "." in args.output_format is being triggered?

Is something wrong with my --to option? Based on the docs (https://jupytext.readthedocs.io/en/latest/config.html), I believe the format above (__sidecar.py:percent) is valid.

Is there a workaround I can use in the meantime? It seems that adding // could fix this, though I don't quite understand how to use it, or if that will cause side-effects?

[mwouts]

Hi @jli again,

Yes you're right, the warning in your case is a bit too much. It is triggered by this condition:

jupytext/jupytext/cli.py

Lines 450 to 457 in 57d83aa

	# Warn if '--to' is used in place of '--output'
	if (
	not args.output
	and args.output_format
	and "." in args.output_format
	and not args.output_format.startswith(".")
	and "//" not in args.output_format
	):

I believe I have not seen this in the Jupytext examples because in my examples the suffix start with a dot. I will see how to improve this, meanwhile you can either ignore the warning, or use a suffix that starts with ..

[jli]

Ah, I see, so the example suffixes look like notebook_name.suffix.py? That seems like a reasonable workaround for us.

Thanks for the quick response!

[mwouts]

From version 1.13.6 on, the warning will not appear any more when the suffix start with either ., - or _. Thanks @jli for pointing out at this.