Hiding the legend for a channel

In vega-lite JSON, under encoding I was able to do the following:

"opacity": {
  "field": "positives",
  "type": "quantitative",
  "legend": false
}

The "legend": false line suppressed the rendering of the opacity legend.

In altair, I tried specifying the following argument for .encode():

opacity = altair.Opacity('positives', legend=False)

This raised the error:

TraitError: The 'legend' trait of an Opacity instance must be a Legend or None, but a value of class 'bool' (i.e. False) was specified.

Any way to hide the legend for a channel in altair?

[jakevdp]

In Altair 2.0, this can be done with legend=None.

[jakevdp]

Altair doesn’t yet support explicit nulls, so now that they have meaning in Vega-Lite we will need to add that. I’d probably opt to introduce an altair.null object for cases like this when the user wants to be explicit (currently None tells Altair to leave that entry out of the schema, and there’s no easy way to change that behavior).