The pyplot package in matplotlib wasn't working on my macbookpro.
It wasn't raising an error, but it wasn't showing a plot either. Pretty much the most frustrating kind of error.
The solution was easy -- once I found it.
Create a file: "~/.matplotlib/matplotlibrc"
and include the line "backend: MacOSX"
and then it works.
StackOverflow has consistently been a great place to find answers to needling problems like this.