Dylan Mikesell found and solved a bug with the python installation on a Mac system where the OS was recently updated. His email informing Fabian of the bug is copied below. Thanks to Dylan for sharing this fix!
I just wanted to give you a heads up about a bug I just ran into after following your python homework.
I recently updated my mac OS and with the latest update it broke jupyter's automatic opening in the web-browser. I found a solution here https://github.com/jupyter/
I don't know if you have any students reporting a problem, but for mac users this will be a problem if they have recently updated their OS.
The solution is like this.
$ jupyter notebook --generate-config
to create ~/.jupyter/jupyter_notebook_
config.py in a text editor and add/set the following line
if using Safari add:
c.NotebookApp.browser = u'Safari'
or if using Chrome add:
c.NotebookApp.browser = u'chrome'
There are a bunch of other comments about setting the default BROWSER, but this worked for me using Safari.