_PropertySetter("title", ...) dynamic doc uses wrong class

[franzhaas]

Dear all,

I tried the example from https://altair-viz.github.io/gallery/layered_chart_with_dual_axis.html, both the Method syntax as well as the Attribute syntax.

On my setup (jupyterlab 4 + altair 5.0.1) only the attribute syntax colours the axis labels with the colours from the graph. The Method syntax colors the axis labels black.

I am happily using the Attribute syntax now. Is this a bug? Of the documentation? Of the library itself?

Thanks in advance,
Franz

---

Minimal Repro

• _PropertySetter("title", ...) dynamic doc uses wrong class #3122 (comment)

[joelostblom]

Thanks for reporting, the reason is that Vega-Lite's title parameter only takes a string, so the title() method (or title= parameter in version <=4) can only take a string of the title text and no parameters for customizing the title (so other parameters such as subtitle= also does not work inside title(). This is currently not clear from the docstring which mentions that it it possible to pass parameters to title, so we should either change the docstring or silently pass those parameters forward to axis(title={}).

Shorter examples:

import altair as alt
from vega_datasets import data

source = data.seattle_weather()


alt.Chart(source).mark_point().encode(
    alt.X('date').title('This should be red', color='red')
)

alt.Chart(source).mark_point().encode(
    alt.X('date').axis(title='This should be red', titleColor='red')
)

[franzhaas]

Ok, thanks this makes sense now...

[franzhaas]

I just checked, it is still an issue with 5.2.0.

[joelostblom]

Yes, this issue will be closed once a PR has been submitted to fix it. Feel free to create one if you have the time to get familiar with the code base.

[dangotbanned]

Closing as #3660 addresses this example

[joelostblom]

@dangotbanned I'll reopen this because it is tracking the general feature of being able to use additional parameters inside .title() just as they can be used inside .axis(title=, ...)

[dangotbanned]

@dangotbanned I'll reopen this because it is tracking the general feature of being able to use additional parameters inside .title() just as they can be used inside .axis(title=, ...)

@joelostblom that's fine with me. Has there been an issue opened upstream for this?

IIRC we would have support for this added "for free" if the vega-lite schema specified TitleParams as an option that is allowed here

[joelostblom]

Has there been an issue opened upstream for this?

I was going to add one right now, but I realized that in the VegaLite spec, maybe this is not much of an advantage as it would be in Altair. E.g. take this spec:

"x": {"field": "date", "title": "A title text", "type": "temporal"}

With out suggestion we are saying it should be possible to pass a dictionary to the "title" key, but that is not too different from what can already be done with axis since there are no positional params in VegaLite's json spec:

# These two options are equally convenient
"x": {"field": "date", "title": {"title": "A title text", "color": "red"}, "type": "temporal"}
"x": {"field": "date", "axis": {"title": "A title text", "color": "red"}, "type": "temporal"}

The difference is more notable in altair since the actual text of the title is passed as a positional argument:

alt.X('date').title("A title text", color="red")
alt.X('date').axis(title="A title text", color="red")

Having that said, it is not a major advantage and I think the biggest issues is that altair suggests it is possible in the docstring to use all the parameters with .title() directly although it isn't:

I see two paths:

1. Fix the .title docstring to indicate that it only takes a string and point users to .axis(title=) for more customization.
2. Do some preprocessing of the schema to always pass everything inside .title() to .axis(title=...) where the first positional argument will be the text of the title.

The second one would be nice, but if the first one is less work then that is a perfectly fine option to me.