Dash for Crime

Using Dash by Plotly for Interactive
Visualisation of Crime Data

Leo Broska -- PyCon AU 2019

Twitter: @halloleo Github: github.com/halloleo

"Just put these numbers into a graph."

Dash by Plotly

What is Dash?
Live demo
More is possible
Wrap it up

What is Dash?

Dash is a framework for building analytical web apps

No JavaScript required.

Plotly

(Plotly Express)

React

Flask

Plotly
React
Flask
Dash

Live Demo

Recap

1. fig = px.line(...

2. @app.callback(...

More is possible

Modularise graphs in components

Many chart types with sensible defaults

Challenges

Multi-page sites awkward to code

Rendering can be slow...

We discovered difficulties with our use case.

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This is only a minor issue but because Dash is geared towards single-page apps it needs additional effort to distribute the charts over multiple pages. So for multi-page app don't expect much help from Dash.

CLICK

More complex Dash apps load a tad slow, because (from my understanding) the JavaScript engine in the browser does a lot of translating of the Python code. Normally that's not a problem, but when you have very slow JavaScript engines (like in IT infrastructures with virtualised desktops) it really shows.

This can be a deal breaker. In our particular environment with virtualised desktops it was a deal breaker. So for the dashboard we did not continue with a Python solution, rather opted for one of the many JavaScript charting libraries, wiring the controls "manually" in JavaScript.

Anyway...

Wrap it up

Dash builds beautiful
analytical web apps

Pure Python. No JavaScript required. Really.

Browser speed critical for
end-user experience

Dash is fun!

Twitter: @halloleo Github: github.com/halloleo