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This is likely because you’re trying to connect to a (presumably non-existent) X-server when you use matplotlib. If you do have X running on your webserver, you probably still want to avoid using an interactive backend for matplotlib
(Edit: Just saw that you’re on windows. Obviously, it’s not that mattplotlib is trying to connect to an X-server when run on Windows, but I’d be willing to bet that your problem is still related to using an interactive backend and matplotlib trying to connect to the graphical display.)
If you want to use matplotlib without interactive plots (i.e. without needing an X-server), then you need to explicitly use a non-interactive backend. (e.g. Agg, pdf, etc)
First off, remove from pylab import *. That’s a really bad idea for a huge number of reasons (hint, min and max aren’t what you think they are, among other things). Also, you don’t seem to be using it. You’re already accessing matplotlib functionality through the pyplot interface and numpy though the numpy namespace.
Next, before you do import matplotlib.pyplot as plt (or before you do from pylab import * if you decide not to remove it), do:
import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot # etc...
Now matplotlib won’t try to connect to the X display everytime you make a new figure.
