Somewhat unhelpful error message when passing a string that does not correspond to a column name

[joelostblom]

What happened?

If I pass a byte string to sort like so:

alt.Chart(pd.DataFrame({'col1': ['c', 'a', 'b']})).mark_point().encode(alt.X('col1').sort(b'cba'))

I'm getting an error messages that says

SchemaValidationError: 'b'cba'' is an invalid value for `sort`. Valid values are:

- One of ['ascending', 'descending']
- One of ['x', 'y', 'color', 'fill', 'stroke', 'strokeWidth', 'size', 'shape', 'fillOpacity', 'strokeOpacity', 'opacity', 'text']
- One of ['-x', '-y', '-color', '-fill', '-stroke', '-strokeWidth', '-size', '-shape', '-fillOpacity', '-strokeOpacity', '-opacity', '-text']
- Of type 'array', 'string', 'object', or 'null'

Notice how the last line mentions that a string can be passed. However, if I do pass a string (that is not an existing column name), that last line of the error message changes to:

- Of type 'array', 'object', or 'null'

I noticed this when reviewing #3501. I'm not sure how important this is and I don't think we should spend a whole lot of time on it, but it is somewhat unhelpful that it is indicated that strings cannot be passed whereas they actually can as long as they correspond to a column/field name. Ultimately we would want a more informative and correct error message, but this is pretty low priority.

What would you like to happen instead?

No response

Which version of Altair are you using?

main