[joelostblom]

Altair actually does introspection when the data is passed as a dataframe (e.g. via pandas or polars). In these cases you can leave out the `:Q` and just write `x='abc'` and Altair will figure out that the encoding type shoudl be quantitative based on the column datatype in the dataframe.

If you are reading the data directly from a URL instead of via a dataframe, the URL is passed on to Vega-Lite and Python never sees the data, so no introspection can be made on the Altair side of things.

(disclaimer: I'm a co-maintainer of Altair)