Cannot override matplotlib format_coord - python-2.7

Question

I'm creating a contour plot with a list of V values as the x-axis and a list of T values as the y-axis (the V and T values are float numbers with 2 digits after the decimal point but all sorted of course). I created a data matrix and populated it with the data correlating with the V-T coordinates.
If it helps anything, this is what the contour plot would look like:
I'm trying to override the format_coord method to also display the data along with the x-y (V-T) coordinates when the cursor moves
I can't post all my code here, but here are the relevant parts:
fig= Figure()
a = fig.add_subplot(111)
contour_plot = a.contourf(self.pre_formating[0],self.pre_formating[1],datapoint) #Plot the contour on the axes
def fmt(x, y):
'''Overrides the original matplotlib method to also display z value when moving the cursor
'''
V_lst = self.pre_formating[0] #List of V points
T_lst = self.pre_formating[1] #List of T points
Zflat = datapoint.flatten() #Flatten out the data matrix
print 'first print line'
# get closest point with known v,t values
dist = distance.cdist([x,y],np.stack([V_lst, T_lst],axis=-1))
print 'second print line'
closest_idx = np.argmin(dist)
z = Zflat[closest_idx]
return 'x={x:.5f} y={y:.5f} z={z:.5f}'.format(x=x, y=y, z=z)
a.format_coord = fmt
The above code does not work (when I move the cursor nothing shows up, even the x,y value. The 'first print line' gets printed but the 'second print line' doesn't, so I think the problem is with the 'dist' line).
But when I change the 'dist' line to
dist = np.linalg.norm(np.vstack([V_lst - x, T_lst - y]), axis=0)
Everything works (x,y,data shows up) for a 37x37 matrix but not for a 37x46 matrix (37T, 46V) and I don't know why.
What should I do to make my code work?
Thank you for helping!

Answer 1

Hi guys so I found out how to solve this in case anyone needs it. There were 2 problems:
1/ I was wrong in my way of generating a list of V,T coordinates
2/ distance.cdist requires everything in the form of a 2d array.
So this is the final solution:
def fmt(x, y):
'''Overrides the original matplotlib method to also display z value when moving the cursor
'''
V_lst = self.pre_formating[0] #List of V points
T_lst = self.pre_formating[1] #List of T points
coordinates = [[v,t] for t in T_lst for v in V_lst] # List of coordinates (V,T)
Zflat = datapoint.flatten() #Flatten out the data matrix
# get closest point with known v,t values
dist = distance.cdist([[x,y]],coordinates)
closest_idx = np.argmin(dist)
z = Zflat[closest_idx]
return 'x={x:.5f} y={y:.5f} z={z:.5f}'.format(x=x, y=y, z=z)