How to adjust size of two subplots, one with colorbar and another without, in pyplot ?

Question

Consider this example

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable

plt.subplot(121)
img = plt.imshow([np.arange(0,1,.1)],aspect="auto")
ax = plt.gca()
divider = make_axes_locatable(ax)
cax = divider.append_axes("bottom", size="3%", pad=0.5)
plt.colorbar(img, cax=cax, orientation='horizontal')
plt.subplot(122)
plt.plot(range(2))
plt.show()

I want to make these two figures (plot region without colorbar) of the same size.

The size is automatically adjusted if the colorbar is plotted vertically or if two rows are used (211, 212) instead of two columns.

Answer 1

One can basically do the same for the second subplot as for the first, i.e. create a divider and append an axes with identical parameters, just that in this case, we don't want a colorbar in the axes, but instead simply turn the axis off.

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable

ax = plt.subplot(121)
img = ax.imshow([np.arange(0,1,.1)],aspect="auto")
divider = make_axes_locatable(ax)
cax = divider.append_axes("bottom", size="3%", pad=0.5)
plt.colorbar(img, cax=cax, orientation='horizontal')

ax2 = plt.subplot(122)
ax2.plot(range(2))
divider2 = make_axes_locatable(ax2)
cax2 = divider2.append_axes("bottom", size="3%", pad=0.5)
cax2.axis('off')
plt.show()

Answer 2

You can now do this without recourse to an extra toolkit by using constrained_layout:

import numpy as np
import matplotlib.pyplot as plt

fig, axs = plt.subplots(1, 2, constrained_layout=True)
ax = axs[0]
img = ax.imshow([np.arange(0,1,.1)],aspect="auto")
fig.colorbar(img, ax=ax, orientation='horizontal')
axs[1].plot(range(2))
plt.show()