Format multi tooltip

Hello, I cannot find a way to provide a format for each field of a multi tooltip. Here is a reproducible example :

import pandas as pd
import numpy as np
import altair as alt

np.random.seed(14)
data = pd.DataFrame({"date": pd.date_range("2018-01-01", periods=100),
                     "values": np.random.normal(size=100)})

alt.Chart(data).mark_point().encode(
    x="date:T",
    y="values:Q",
    tooltip=alt.Tooltip(['date:T', 'values:Q'], format='.2f')
)

Which formats also the date field: If I try something like

alt.Tooltip(['date:T', 'values:Q'], format=['%d/%m/%Y', '.2f'])

I have an error saying that format is not a string.

So, how can I specify the format of each field in this multi tooltip ?

[jakevdp]

You can set the encoding to a list of alt.Tooltip objects, each with their own format string:

import pandas as pd
import numpy as np
import altair as alt

np.random.seed(14)
data = pd.DataFrame({"date": pd.date_range("2018-01-01", periods=100),
                     "values": np.random.normal(size=100)})

alt.Chart(data).mark_point().encode(
    x="date:T",
    y="values:Q",
    tooltip=[alt.Tooltip('values:Q', format='.2f'),
             alt.Tooltip('date:T', format='%A, %B %e')]
)

[tonylee3399]

Just for additional information, if you need to show DateTime format in your tooltip, you could refer to this d3-time-format