.ipynb file is an IPython Notebook file containing the Python commands, output and notes that another user has recorded.
To be able to create or open this file, we need to install IPython and its notebook package:
$ sudo apt install ipython-notebook
After installation, it is invoked as:
$ ipython notebook
This open a Mathematica-like web interface in your browser. You can create new IPython Notebook files or open existing files for viewing.
On a recent IPython Notebook file, I got this error when I opened it:
Error loading notebook Unreadable Notebook: Unsupported JSON nbformat version 4 (supported version: 3)
This means that a more recent version of notebook package needs to be used to open this file. More confusingly, the notebook package has been moved into a new project called Jupyter. Since this is a new development its package was not available on my ancient Ubuntu.
I installed it from PyPI using:
$ sudo pip3 install jupyter
To open its notebook web interface:
I was able to open the problematic IPython Notebook file correctly using this.
Tried with: Jupyter 4.x and Ubuntu 14.04