Altair plot in Plotly Dash

altair_app.py

# -*- coding: utf-8 -*-
import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import pandas as pd
import sqlalchemy
import altair as alt
import io
from vega_datasets import data

# Don't need this with the cars dataset
alt.data_transformers.enable('default', max_rows=10000)

# Not using sql here
# conn = sqlalchemy.create_engine()

cars = data.cars()

app = dash.Dash(__name__, static_folder='assets')
app.css.append_css({'external_url':
                    'https://cdn.rawgit.com/gschivley/8040fc3c7e11d2a4e7f0589ffc829a02/raw/fe763af6be3fc79eca341b04cd641124de6f6f0d/dash.css'
                    })
app.title = 'Test dash and altair'
server = app.server


app.layout = html.Div([
    html.Div([

    html.P([
        html.Label('x-axis'),
        # dcc.Input(id='mother_birth', value=1952, type='number'),
        dcc.Dropdown(
            id='x_axis',
            options=[{'label': i, 'value':i} for i in cars.columns],
            value='Acceleration'
        )
    ],
    style={'width': '250px', 'margin-right': 'auto',
           'margin-left': 'auto', 'text-align': 'center'}),
    html.P([
        html.Label('y-axis'),
        # dcc.Input(id='mother_birth', value=1952, type='number'),
        dcc.Dropdown(
            id='y_axis',
            options=[{'label': i, 'value':i} for i in cars.columns],
            value='Miles_per_Gallon'
        )
    ],
    style={'width': '250px', 'margin-right': 'auto',
           'margin-left': 'auto', 'text-align': 'center'})],
           className='input-wrapper'),


    html.Iframe(
        id='plot',
        height='500',
        width='1000',
        sandbox='allow-scripts',

        # This is where we will pass the html
        # srcDoc=

        # Get rid of the border box
        style={'border-width': '0px'}
    )
])

@app.callback(
    dash.dependencies.Output('plot', 'srcDoc'),
    [dash.dependencies.Input('x_axis', 'value'),
     dash.dependencies.Input('y_axis', 'value')]
)
def pick_figure(x_axis, y_axis):

    brush = alt.selection_interval()

    points_cars = alt.Chart(cars).mark_point().encode(
        x=x_axis,
        y=y_axis,
    ).properties(
        width=250,
        height=250,
        selection=brush
    )

    bars = alt.Chart(cars).mark_bar().encode(
        x='Horsepower:Q',
        y='count()'
    ).transform_filter(
        brush.ref()
    )

    chart = alt.hconcat(points_cars, bars)
    
    # Save html as a StringIO object in memory
    cars_html = io.StringIO()
    chart.save(cars_html, 'html')
    
    # Return the html from StringIO object
    return cars_html.getvalue()



if __name__ == '__main__':
    app.run_server(debug=True)

Had a lot of trouble getting this running because string values being passed into srcDoc were causing vega issues from Altair but the html works just fine. So used src attribute and opened the html (not string version to html! but just straight to html file itself) and it worked.

Many thanks, helped me a lot with my project!