Python Altair, query for current axis limits - python-3.x

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'].