Using matplotlib.animate to animate a contour plot in python

I have a 3D array of data (2 spatial dimensions and 1 time dimension) and I'm trying to produce an animated contour plot using matplotlib.animate. I'm using this link as a basis:

http://jakevdp.github.io/blog/2012/08/18/matplotlib-animation-tutorial/

And here's my attempt:

import numpy as np
from matplotlib import pyplot as plt
from matplotlib import animation
from numpy import array, zeros, linspace, meshgrid
from boutdata import collect

# First collect data from files
n = collect("n")   #  This is a routine to collect data
Nx = n.shape[1]
Nz = n.shape[2]
Ny = n.shape[3]
Nt = n.shape[0]

fig = plt.figure()
ax = plt.axes(xlim=(0, 200), ylim=(0, 100))
cont, = ax.contourf([], [], [], 500)

# initialisation function
def init():
    cont.set_data([],[],[])
    return cont,

# animation function
def animate(i): 
    x = linspace(0, 200, Nx)
    y = linspace(0, 100, Ny)
    x,y = meshgrid(x,y)
    z = n[i,:,0,:].T
    cont.set_data(x,y,z)
    return cont, 

anim = animation.FuncAnimation(fig, animate, init_func=init,
                           frames=200, interval=20, blit=True)

plt.show()

But when I do this, I get the following error:

Traceback (most recent call last):
  File "showdata.py", line 16, in <module>
    cont, = ax.contourf([], [], [], 500)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 7387, in contourf
    return mcontour.QuadContourSet(self, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/contour.py", line 1112, in __init__
    ContourSet.__init__(self, ax, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/contour.py", line 703, in __init__
    self._process_args(*args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/contour.py", line 1125, in _process_args
    x, y, z = self._contour_args(args, kwargs)
  File "/usr/