Line Chart with datum

An example of using datum to highlight certain values, including a DateTime value. This is adapted from two corresponding Vega-Lite Examples: Highlight a Specific Value.

import altair as alt
from vega_datasets import data

source = data.stocks()

lines = (
    .encode(x="date", y="price", color="symbol")

xrule = (
    .mark_rule(color="cyan", strokeWidth=2)
    .encode(x=alt.datum(alt.DateTime(year=2006, month="November")))

yrule = (
    alt.Chart().mark_rule(strokeDash=[12, 6], size=2).encode(y=alt.datum(350))

lines + yrule + xrule