Your currently selected backend, ‘agg’ does not support show().
AGG backend is for writing to file, not for rendering in a window. See the backend FAQ at the matplotlib web site.
ImportError: No module named _backend_gdk
For the second error, maybe your matplotlib distribution is not compiled with GTK support, or you miss the PyGTK package. Try to install it.
Do you call the
show() method inside a terminal or application that has access to a graphical environment?
Try other GUI backends, in this order: