import numpy as np

import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import AxesGrid
import matplotlib as mpl

levels = np.arange(0., 1.2, 0.15)

# This yields blank values just before the end arrows in the colorbar.
fig = plt.figure()
axgrid = AxesGrid(fig, 111, 
                  nrows_ncols=(1, 1), 
                  ngrids=1,
                  cbar_mode='single')
ax = axgrid[0]
cs = ax.contourf(np.random.random((10, 20)),
                 extend='both')
cbar = axgrid.cbar_axes[0].colorbar(cs)

# This problem does not occur when not using AxesGrid.
fig, ax = plt.subplots()
cs = ax.contourf(np.random.random((10, 20)),
                 extend='both')
cbar = plt.colorbar(cs, ax=ax)

# The problem also doesn't occur if using AxesGrid + manually creating the colorbar.
fig = plt.figure()
axgrid = AxesGrid(fig, 111, 
                  nrows_ncols=(1, 1), 
                  ngrids=1,
                  cbar_mode='single')
ax = axgrid[0]
cs = ax.contourf(np.random.random((10, 20)),
                 extend='both', levels=levels)

cmap = mpl.cm.viridis
cb = mpl.colorbar.ColorbarBase(axgrid.cbar_axes[0], cmap=cmap,
                               boundaries=levels,
                               orientation='vertical', extend='both')