Jake Vanderplas

Creating a PNG requires a javascript runtime: the mimetype extension accesses this via the jupyterlab frontend. That's not generally available for Python runtimes, and even for Python runtimes that are...

I think a more fruitful approach to improving `altair_saver` would be to wrap Kaleido; see https://github.com/altair-viz/altair_saver/issues/85

Just for reference, here is the code used by `alt.renderers.enable('notebook')` to embed the PNG in the mimebundle output: https://github.com/vega/ipyvega/blob/v2.5.0/src/index.ts#L65-L93 For jupyterlab there is a similar code path.

I've been worried about adding this sort of thing because the failure mode in which we remove a column that's needed by the chart is something that can't easily be...

One situation I can think of is column names with special characters that may or may not be escaped when referenced in the chart spec. You could also construct column...

Here's an example that would break with this PR, I believe: ```python import altair as alt import pandas as pd df = pd.DataFrame({'somecolumn': [1, 2, 3, 4]}) alt.Chart(df).transform_calculate( data='datum["some" +...

Even with an escape hatch, I’m not sure we’d want to land this change. Imagine the headache of trying to write some non-trivial Vega expression and finding after an hour...

Sure, opt-in would be better, but then 99% of users would never know the feature exists and never benefit from it. I think better would be to avoid the easy...

conditions are only supported for encodings, unfortunately.

FYI: for the power user, often the best way to answer "is this possible" questions is to look at the vega-lite schema. For example, here it's clear that ``dy`` can...