Correctly display prompt numbers that are 'None'

[jhamrick]

Fixes #6702

[minrk]

Would it be possible to add tests to catch regressions?

[jhamrick]

I can definitely add tests for the live notebook. I'm not sure what the best way to test for it in the HTML/LaTeX output would be though -- maybe a regex match for the In: and Out: prompts?

[jhamrick]

Ok, tests added. The one thing I didn't do though was add tests for the style_bw_ipython.tplx template, because it doesn't seem like it's being used anywhere so I'm not sure how to get nbconvert to use it instead of style_ipython.tplx. I could create a custom template in the tests folder (instead of article.tplx or report.tplx) but that feels hacky somehow?

[takluyver]

I think it's OK to leave that case untested.

[takluyver]

I think checking that the prompts exactly match this is a bit brittle, because if you e.g. add one cell for another test, this will break. I'm not sure what's a good way to write the test, though.

[jhamrick]

Yeah, true. I could create a new notebook in files/ that's specifically for testing prompt numbers, and is therefore less likely to be changed unless the prompt numbering tests are also changed.

[takluyver]

That sounds reasonable.

[jhamrick]

Done.

[takluyver]

Can we cut the prompt numbers test notebook down to just enough cells to test the different possibilities for prompt numbers? That just makes it clear what it's there for.

[jhamrick]

Yup. Now it just includes cells/tests for: single-digit prompt number, double-digit prompt number, output prompt number, no prompt number, null prompt number, asterisk, and zero prompt number.

[takluyver]

Excellent, thanks. Merging.

[jhamrick]

Sweet, thanks!

[jhamrick]

Hmm, this is still a problem on nbviewer though because it's running 2.3.0. Should this be backported, or just wait for 3.0?