This works well for me:
from matplotlib import pyplot as plt
F = gcf()
Size = F.get_size_inches()
F.set_size_inches(Size[0]*2, Size[1]*2, forward=True) #Set forward to True to resize window along with plot in figure.
plt.show() #or plt.imshow(z_array) if using an animation, where z_array is a matrix or numpy array
This might also help: http://matplotlib.1069221.n5.nabble.com/Resizing-figure-windows-td11424.html
