Ensure stdout works in Jupyter Notebooks

[manics]

sys.stdout in Jupyter notebooks may not have a buffer attribute.

To test: run create_companion(images=[companion]) (i.e. use the default out parameter) in a Jupyter Notebook.

See e.g. Yelp/mrjob#1443

[sbesson]

Changes makes sense. Just one explanatory line about the context of the change would be useful. Otherwise LGTM.

Outside the scope of this PR, do you know of some mechanism allowing to test minimal Jupyter notebooks in a tox environment?

[sbesson]

👍 especially as setup.py forces Python3+

[sbesson]

Happy with either the try/catch approach or the getattr one-liner.

Is it possible to add a comment similar to Yelp/mrjob#1443 explaining the special handling? Is there a reference page explaining why the stdout is different in the Jupyter notebook environment?

[manics]

Updated. I'm not aware of an explanation, my best guess is it was originally written to match python2 sys.stdout and no one thought of adding .buffer to it.

[manics]

For testing you can use nbval, for example
https://github.com/IDR/idr-notebooks/blob/master/docker/test_notebooks.sh
though note this script isn't yet automatically run in travis on that repo.