You are already fixing the size of your plot with divider.append_axes("right", 1.2, pad=0.1, sharey=axMain)
. 1.2 is the size of the new axis. Below is a way of plotting three axes using gridspec
.
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.gridspec as grd
from numpy.random import rand
# add axes
fig1 = plt.figure(1)
gs = grd.GridSpec(1, 3, width_ratios=[5,1, 1], wspace=0.3)
axMain = plt.subplot(gs[0])
axHisty = plt.subplot(gs[1])
ax_cb = plt.subplot(gs[2])
# some things to plot
x = [1,2,3,4]
y = [1,2,3,4]
x1 = [1,2,3,4]
y1 = [1,2,3,4]
z1 = rand(4,4)
# make plots
h = axMain.contourf(x1,y1,z1)
axHisty.plot(x,y)
cb = plt.colorbar(h, cax = ax_cb)
plt.show()