Problem with numpy 2D Histogram

[Jamie Mitchell]

Hi folks,

I'm trying to plot a 2D histogram but I'm having some issues:
from pylab import *
import numpy as np
import netCDF4
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
extent=[xedges[0],xedges[-1],yedges[0],yedges[-1]]
imshow(hist.T,extent=extent,interpolation='nearest')
colorbar()
show()

After the first line of code I get:
TypeError: Cannot cast array data from dtype('O') to dtype('float64') according to the rule 'safe'

I'm using python2.7, x and y are type 'numpy.ndarray'

Cheers,
Jamie