Altair: Default Mark Property

[nielsmde]

I came accross a problem with the display of altair plots in Jupyter notebooks.
Take the following code, where df is any dataset:

from altair import Chart
Chart(df).to_dict().get('mark')

This would return 'point' in altair 1.0.0. In altair 1.2.0 this returns None, which results in a javascript error of the jupyter-vega extension and no display of the plot.

If the latter behavior is anticipated (i.e. the mark property of vega-lite plots may be undefined) the jupyter-vega extension would need a fix.

Niels

[jakevdp]

Thanks! Yes, I'd noticed that changed, but hadn't appreciated the consequences. We'll make sure to fix this in the upcoming 2.0 release.

[ellisonbg]

I marked this as 1.3 as it should be easy to fix.