from matplotlib import colors
import matplotlib.pyplot as plt

grid = np.linspace(-1., 1., 100)
fig, ax = plt.subplots(1, 1, figsize=(5,5))
fig = pot.plot_contours(grid=(grid,grid), cmap='Blues',
                        levels=np.logspace(-3, 1, 10),
                        norm=colors.LogNorm(), ax=ax)