IPython and Javascript interaction

This IPython notebook demonstrates the interaction between Python and a popup window that is opened via Javascript. The interaction is one-way in this case, from the notebook to the popup. We write data to the popup and call functions in the popup by executing Javascript from within the notebook. The goal is to demonstrate some simple interactions. In the end, I hope that techniques like these could be used for livecoding in Python, with a HTML5 visualization window.

First, the notebook server and the HTML that we load in the popup must be located on the same domain. For this, we need to copy the index.html to the root directory of the IPython server. Unfortunately, it is not easy to find out what the root directory is. The default is the home directory of the user, so if you didn’t mess with your config just copy the html file to your home directory. If you changed your config you probably know whether you changed the root (it’s the setting ipython_dir).

The index.html contains an empty D3 scatterplot that we will fill with data from within this notebook. The notebook is available on Github here:

https://github.com/pbouda/stuff/blob/master/ipynb/Javascript%20Interactions%20I.ipynb

Open a browser popup

IPython contains several helper methods in IPython.display to output HTML, Javascript, etc. to the current cell’s output. We use those helpers to write Javascript that opens a popup window. We save a reference to the opened window in window.audiencePopup. We can later access the open popup via this reference. First, we open some URL to see if something simple works:

from IPython.display import HTML, Javascript, display
js = """window.audiencePopup = window.open('http://www.heise.de','audienceWindow');"""
display(Javascript(js))

Change the location

We are now able to change the URL of the popup. We set the URL to the local index.html that you downloaded above. We have to prepend /files/ so that the IPython server knows that we are looking for a local, static file. The notebook server then serves this file to the popup window:

js = """window.audiencePopup.location.href = "/files/index.html";"""
display(Javascript(js))

As said above, the index.html has to be served from the same domain as your current IPython notebook for security reasons. If everything works than you should now see the empty scatterplot in the popup.

Write some data to the popup

We will now write some data to the popup. If you look into index.html you will see a Javascript variable data that contains an empty list. The scatterplot is created from coordinates in that list. In the first step we will set the data variable to a Python list of coordinates. For this we just have to convert the Python list to a JSON string and set the Javascript variabel to a parsed version of that JSON string. We use the Javascript function JSON.parse:

import json
data = [ [0, 0], [1, 1], [0.5, 0.5] ]
js = """window.audiencePopup.data = JSON.parse('{0}');""".format(json.dumps(data))
display(Javascript(js))

The scatterplot don’t change, because we have to tell it to update itself first. But you can already have a look the the content of the data variable in the popup window. We just display the value in an alert window:

js = """alert(window.audiencePopup.data);"""
display(Javascript(js))

The index.html also containts a function update() that we can just call to repaint the scatterplot. Again, we are able to call this Javascript function directly from within the current notebook:

js = """window.audiencePopup.update();"""
display(Javascript(js))

You should now see the data points in the scatterplot. You can see a screencast where I execute this notebook here:

About me

My name is Peter Bouda and I am and Angular/JavaScript coach and consultant with more than 15 years of professional experience in web application development. I help you to bring your web product to market as quickly as possible.

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