Option for not writing an output ipynb file

[dcnadler]

What does this PR do?

In the current setup of papermill, an output_path is required to write an output ipynb file even if you only want to use the returned NotebookNode object. For example, in my case, I end up using tempfile a good amount to get around this.

This motivation came up in PR #107, as well

Approach

Let user pass output_path = None to indicate they don't want to write an output ipynb.

A new IO handler was added, NoIOHandler to deal with this option.

Alternative approach

I tried to match the api interface of PR #107, but I could also see having a specific string that indicates no output writing (similar to "-" indicating stdin/stdout).

The advantage being that the IO handler can be registered in the IO factory as designed, and not implemented outside of it as I had to do with path=None, since get_handler uses path.startswith.

If that sounds like a better approach, I'm open to string suggestions - haven't thought of a good one yet :)

[MSeal]

Thanks, this seems like a cleaner way than doing '/dev/null' output pathing.

[codecov]

Codecov Report

Merging #669 (bb587e0) into main (a6b00a8) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #669      +/-   ##
==========================================
+ Coverage   91.64%   91.72%   +0.07%     
==========================================
  Files          17       17              
  Lines        1568     1583      +15     
==========================================
+ Hits         1437     1452      +15     
  Misses        131      131              

Impacted Files	Coverage Δ
papermill/execute.py	100.00% <ø> (ø)
papermill/iorw.py	80.23% <100.00%> (+0.80%)	⬆️
papermill/parameterize.py	97.95% <100.00%> (+0.08%)	⬆️

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[mnp]

How does one do this from the CLI?

Seems like passing /dev/null would be fine but you get a warning when it doesn't know that file extension.

[dcnadler]

This PR did modify the CLI interface.

If you wanted to add a no-output CLI option, it looks like you'd need to add that in https://github.com/nteract/papermill/blob/main/papermill/ and work around the stdout logic.