Python Altair, query for current axis limits

Question

I know how to set axis limits and whatnot, but how do I query for currently used axis limits?

Answer 1

I don't think this is possible unless you specifically set an axis limit first:

import altair as alt
from vega_datasets import data

source = data.cars.url

chart = alt.Chart(source).mark_circle().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
)

chart.to_dict()

{'config': {'view': {'continuousWidth': 400, 'continuousHeight': 300}},
 'data': {'url': 'https://cdn.jsdelivr.net/npm/vega-datasets@v1.29.0/data/cars.json'},
 'mark': 'circle',
 'encoding': {'x': {'field': 'Horsepower', 'type': 'quantitative'},
  'y': {'field': 'Miles_per_Gallon', 'type': 'quantitative'}},
 '$schema': 'https://vega.github.io/schema/vega-lite/v5.2.0.json'}

If you set the domain, you can see it in the spec:

chart = alt.Chart(source).mark_circle().encode(
    x=alt.X('Horsepower:Q', scale=alt.Scale(domain=[0, 250])),
    y='Miles_per_Gallon:Q',
)

chart.to_dict()

{'config': {'view': {'continuousWidth': 400, 'continuousHeight': 300}},
 'data': {'url': 'https://cdn.jsdelivr.net/npm/vega-datasets@v1.29.0/data/cars.json'},
 'mark': 'circle',
 'encoding': {'x': {'field': 'Horsepower',
   'scale': {'domain': [0, 250]},
   'type': 'quantitative'},
  'y': {'field': 'Miles_per_Gallon', 'type': 'quantitative'}},
 '$schema': 'https://vega.github.io/schema/vega-lite/v5.2.0.json'}

and get it via chart.to_dict()['encoding']['x']['scale']['domain'].