Customizing Renderers

Renderers in Altair are all based on the mimebundle representation accessed by the _repr_mimebundle_ method of the top-level Altair objects. When you enable a renderer, functionally what that does is to define a new kind of mimebundle output.

The alt.renderers registry allows the user to define and enable new mimetypes for the chart. As a simple example, imagine we would like to add a plaintext renderer that renders a chart description in plain text. We could do it this way:

def plaintext_mimetype(spec):
    return {'text/plain': "description: " + spec.get('description', 'none')}

alt.renderers.register('plaintext', plaintext_mimetype)

Now you can enable this mimetype, and then when your chart is displayed you will see this description:

alt.renderers.enable('plaintext')

alt.Chart('data.txt').mark_point().encode(
    x='x:Q',
    y='y:Q'
).properties(
    description='This is a simple chart'
)

description: This is a simple chart

This is a simple example, but it shows you the flexibility of this approach. If you have a frontend that recognizes _repr_mimebundle_ as a means of obtaining a MIME type representation of a Python object, then you can define a function that will process the chart content in any way before returning any mimetype.

The renderers built-in to Altair are the following:

• "default": default rendering, using the 'application/vnd.vegalite.v2+json' MIME type which is supported by JupyterLab and nteract.

• "html": identical to "default"

• "mimetype": outputs a vega-lite specific mimetype together with a PNG representation.

• "jupyterlab": identical to "mimetype"

• "nteract": identical to "mimetype"

• "colab": renderer for Google’s Colab notebook, using the "text/html" MIME type.

• "notebook": renderer for the classic notebook, provided by the ipyvega package

• "json": renderer that outputs the raw JSON chart specification, using the 'application/json' MIME type.

• "png": renderer that renders and converts the chart to PNG, outputting it using the 'image/png' MIME type.

• "svg": renderer that renders and converts the chart to an SVG image, outputting it using the 'image/svg+xml' MIME type.