Why not make the expressions available as attributes on the top level import?

There might be a good reason for this I’m ignorant of, but wouldn’t it be nicer if you could do this:

import altair as alt
print(alt.datum) # <-- Just dummy code to illustrate accessing datum for use

Instead of this:

import altair as alt
from altair.expr import datum
print(datum)

Why not structure the expressions like datum in a way that they are available to the alt object without requiring a second import?

[jakevdp]

In any case, I don’t think it makes sense to break conventions with the choices made in Vega-Lite, so I’m going to close this.

[jakevdp]

The reason it should not be symmetric with the data argument that you pass toChart is that you’re not doing operations on the entire data set! You’re doing operations on one element at a time within one column of the data, for which “datum” seems a reasonable choice of nomenclature as any.