Working standalone example

[floli]

Hello,
I just started to explore Altair, together with Marimo. Plotting in marimo works basically, but I also wanted to try standalone scripts. However, I was completely unable to produce any output:

import altair as alt
import pandas as pd

# tried some other ones: mimetype, png
alt.renderers.enable("browser")

source = pd.DataFrame({
    'a': ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'],
    'b': [28, 55, 43, 91, 81, 53, 19, 87, 52]
})

alt.Chart(source).mark_bar().encode(
    x='a',
    y='b'
)
# tried to add a .show(), that seems to be required sometimes.

I tried running inside and outside of VS code.

My system is Mac OS. The script never produces any output / opens a browser fenster / writes a file.

What is missing there?

Thanks a lot!

[mattijn]

Did you try chart.save()? See https://altair-viz.github.io/user_guide/saving_charts.html

[floli]

I am able to get the chart to a HTML file using:

with open("output.html", "w") as f:
    alt.Chart(source).mark_bar().encode(x="a", y="b").save(f, "html")

Still, I wonder how to get the to the browser interface, i.e. alt.renderers.enable("browser")

[mattijn]

Good question. I remember it is possible, and found the corresponding PR again, it is here: #3379. If you are on Altair version 5.3.0 or later this should be possible.

When I place the following python code in a file named test_render.py and run the script with python from within the terminal (python ./test_render.py) it is actually opening a new browser window as requested. And when I re-run the script from the terminal after changing the data within the chart it refreshes the browser window that is already open.

import altair as alt
import pandas as pd

alt.renderers.enable("browser", using="safari", port=3001)

source = pd.DataFrame({
    'a': ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'],
    'b': [28, 55, 43, 91, 81, 53, 19, 87, 52]
})

chart = alt.Chart(source).mark_bar().encode(
    x='a',
    y='b'
)
chart.show()

See also the following recording from a terminal within Jupyter-lab (I tried the normal terminal as well and that also works for me)

Screen.Recording.2025-02-01.at.20.35.08.mov

Relevant docs are here: https://altair-viz.github.io/user_guide/display_frontends.html#display-browser

When used in IPython-based environments, the "browser" renderer will automatically open the chart in the browser when the chart is the final value of the cell or command. This behavior is not available in the standard python REPL. In this case, the chart.show() method may be used to manually invoke the active renderer and open the chart in the browser.