Can we reduce the number of false-positives of the `user warning: automatically deduplicated selection parameter`

[mattijn]

What happened?

With the release of altair version 6.0.0, we now raise a user warning in situations described here #3891:

This user warning looks as such:

UserWarning: Automatically deduplicated selection parameter with identical configuration. 
If you want independent parameters, explicitly name them differently (e.g., name='param1', name='param2').
See https://github.com/vega/altair/issues/3891
  exec(compiled, namespace)

When building the docs, see for example this GitHub actions (open Build docs and scroll the loggings), I noticed that this user warning is raised several times as a false-positive. In most of these cases we are re-using the same selection, such as in a layered or concatenated chart. In that case we can safely ignore the warning, while Altair is just letting us know that it merged the identical definitions for us.

What would you like to happen instead?

But what if I don't want a warning? How do I change my specification to not have this? And, can we find ways to reduce the number of false-positives of these user warnings?

Which version of Altair are you using?

Altair version 6.0.0

[joelostblom]

One solution could be to introduce a configuration option related to controlling the warnings similar to have we have alt.data_transformers.disable_max_rows() and a few others (similar to numpy's errstate). We would need to decide whether that is enough benefit over just using the built-in Python warnings module to ignore a specific warning.

Another solution could be to explore if some of the examples could be re-written in a more idiomatic manner that doesn't raise the warning. If we take the linked scatter plot gallery spec as an example, instead of adding the parameter to the base chart and then concatenating two base charts each containing the same parameter, the param could be added just to the concatenated chart? So the last line would instead read:

(base.encode(x='Horsepower') | base.encode(x='Acceleration')).add_params(brush)

At least I thought this would work, but it seems to still raise the warning. That's a bit confusing since the syntax above suggest that a single parameter is added to the concatenated chart (rather than separately added to each chart and then combined).