docs: Add example for *Bar Chart with Highlighting on Hover and Selection on Click*

[dangotbanned]

Fixes #3301

Utilises alt.when, introduced in #3427

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@mattijn I thought adding this first would be something to refer to in the follow-up PR discussed in #3427 (comment)

Also revisiting since #2759 (comment) I have a better explanation for the empty=False placement.

For select, the Parameter is used twice - once with empty=False and another with the default.
Whereas highlight is used only once.

I think this could be helpful to add to the alt.condition(empty) and each .when(empty) doc, as this is a good justification for why you can pass empty there.

https://github.com/dangotbanned/altair/blob/ef81573b9c709989d3965f778a5b0c5d77f6d4c3/tests/examples_methods_syntax/interactive_bar_select_highlight.py#L26-L45

[mattijn]

Thanks! If you have more insight where to place empty=False, that would be great. I thought we could control everything within the alt.selection_point(), but that seems not to be the case.

I added two suggestions that shows on a single line the when().then()'s

[dangotbanned]

Thanks! If you have more insight where to place empty=False, that would be great. I thought we could control everything within the alt.selection_point(), but that seems not to be the case.

I added two suggestions that shows on a single line the when().then()'s

Thanks for the review @mattijn

stroke_width = (
    alt.when(select).then(alt.value(2, empty=False))
    .when(highlight).then(alt.value(1))
    .otherwise(alt.value(0))
)

I've no strong feelings on the formatting (happy to change), but two points I wanted to mention:

1. I simply ran:

>>> ruff format ./tests/*/interactive_bar_select_highlight.py

I did notice ruff seems to be disabled for the examples, so if this changed in the future - we'd end up back at the original.

2. If a user copies the example, and is using ruff | black - they may find the result surprising/unfamiliar.

---

I would say generally though I'd be in favor of running all the examples through ruff, for greater consistency:

• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/hexbins.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/distributions_and_medians_of_likert_scale_ratings.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/bar_chart_with_range.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/area_chart_gradient.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/candlestick_chart.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/comet_chart.py
• https://github.com/vega/altair/blob/80939e74ef4b5b2fc2c5dbb9ea30d2478d523b9c/tests/examples_arguments_syntax/dendrogram.py

[mattijn]

From a programming perspective I can understand that you just want to ruff everything.
But the reason why autoformatting is disabled on the examples is because the autoformatted syntax is often producing results of altair syntax that I would not advocate in writing as a user. If the user decide to autoformat the code once finished, that is fine by me. What do you think?

[dangotbanned]

What do you think?

@mattijn all good with me, I'll accept the suggestions and we can get this merged

[dangotbanned]

@mattijn https://mypy-lang.blogspot.com/2024/07/mypy-111-released.html?m=1

🤦

[dangotbanned]

#3487 will fix the unrelated mypy issue

[mattijn]

Thanks! Tests pass now🥳