django-vega
install
pip install django-vega
usage
from django_vega.views import AltairTemplateView
from .models import Sale
import altair as alt
class SaleView(AltairTemplateView):
queryset = Sale.objects.all().values('date', 'amount', 'payment_method')
chart_title = 'All Sales'
embed_options = {
'renderer': 'svg'
}
def get_chart(self):
return alt.Chart(self.get_data()).mark_circle().encode(
x='date:T',
y='amount:Q',
color='payment_method:N'
)server rendering
Server rendering to svg and png is done with headless chromium. Ensure your system has a recent version installed. Depending on your expected workload, you will either want to keep a browser process running in the background, or start a short-lived instance for each render.
The render function will return both an SVG string and a base64-encoded PNG.
Should a headless chromium instance be spawned, pass a path to the executable via the spawn argument. The alternative
is to have a running instance at port 9222.
import base64
from django_vega import render
spec = {
"$schema": "https://vega.github.io/schema/vega-lite/v3.json",
"description": "A simple bar chart with embedded data.",
"data": {
"values": [
{"a": "A","b": 28}, {"a": "B","b": 55}, {"a": "C","b": 43},
{"a": "D","b": 91}, {"a": "E","b": 81}, {"a": "F","b": 53},
{"a": "G","b": 19}, {"a": "H","b": 87}, {"a": "I","b": 52}
]
},
"mark": "bar",
"encoding": {
"x": {"field": "a", "type": "ordinal"},
"y": {"field": "b", "type": "quantitative"}
}
}
result = render(spec, spawn='/Applications/Chromium.app/Contents/MacOS/Chromium')
with open('image.png', 'wb') as f:
b = base64.b64decode(result['png'])
f.write(b)
with open('image.svg', 'w') as f:
f.write(result['svg'])
testing
A test Django application is located in the test folder.
Automated testing is on the todo list.
