Why am I suddenly having a Python bouncing rocket?

Question

I recently made a simple replacement for some matplotlib code that I run on OS X (10.10; Python 2.7.6), commenting out one line that sets the backend that I use

#matplotlib.use('agg') 

Now, while my code is running, I get a bouncing Python icon in my dock that does not display the user interface and only offers Force Quit ... as a command:

Typically, dock icons that continue to bounce without any interface are bad. Why am I getting this and this is what I should worry about?

Answer 1

Not a "bad thing." The icon appears on the dock when Python interacts with the GUI. Agg is a non-interactive backend. With agg you did not see the icon, since there was no interaction with the Python UI.