Python Altair Load from JSON

user_14890683 0
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looking for help on how to load an altair chart from a json file (contains dict_keys(['$schema', 'config', 'datasets', 'title', 'vconcat'])).

The json file was created using the altair.Chart method to_json() such as below:

import altair as alt


chart = alt.Chart(df).mark_line(...).encode(...).properties(...).transform_filter(...)
chart_json = chart.to_json()

Here is a sample of the code I would like to run

chart = alt.load_json(chart_json)  # made-up, needs replacement
chart.save('chart.png')

Disclaimer: I've never used altair and am trying to reverse-engineer a project. Thanks in advance for the help!

altair python json
2 Answers

Altair can work directly with json files by specifying their path/url as shown in the documentation:

import altair as alt
from vega_datasets import data


url = data.cars.url  # URL/path to json data

alt.Chart(url).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q'
)

To load a local file, there are several potential issues, including the browser having access to local files and using the correct format for the frontend you're using (e.g. jupyterlab). These have been elaborated on elsewhere:

user_21668230

It sounds like you're looking for the alt.Chart.from_json method:

new_chart = alt.Chart.from_json(chart_json)
new_chart.display()

The method assumes that chart_json is a string of JSON representing a valid Altair chart.

user_29378310
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