Why are the subplots in the subfigures getting smaller?

Question

I am using gridspec within a subfigure. For some reason matshow plots are getting smaller and smaller.

import numpy as np
import matplotlib.pyplot as plt

mask = np.array([
        [ 1, 0, 1, 0, 1],
        [ 1, 1, 1, 1, 1],
        [ 0, 0, 0, 0, 0],
        [ 1, 1, 1, 1, 1],
        [ 1, 1, 1, 1, 0]
])   
    
fig = plt.figure(figsize = (12,16), layout = "constrained")
figures = fig.subfigures(4, 2)
figures = figures.reshape(-1)
x = np.linspace(0, 1, 100)
y = x**(0.5)

for f in figures:
    spec = f.add_gridspec(3, 2)
    for i in range(3):
        image_axis = f.add_subplot(spec[i, 0])
        image_axis.matshow(mask, cmap = 'grey')
    plot_axis = f.add_subplot(spec[:,1])
    plot_axis.plot(x, y)

plt.savefig('test.png')

Answer 1

This is an annoyance with constrained layout. However, the easiest solution is to nest the subfigures yet again:

import numpy as np
import matplotlib.pyplot as plt

mask = np.array([
        [ 1, 0, 1, 0, 1],
        [ 1, 1, 1, 1, 1],
        [ 0, 0, 0, 0, 0],
        [ 1, 1, 1, 1, 1],
        [ 1, 1, 1, 1, 0]
])

fig = plt.figure(figsize = (12,16), layout = "constrained")
figures = fig.subfigures(4, 2)
figures = figures.reshape(-1)
x = np.linspace(0, 1, 100)
y = x**(0.5)

for f in figures:
    subsubfigs = f.subfigures(1, 2)
    imaxs = subsubfigs[0].subplots(3, 1)
    for i in range(3):

        imaxs[i].matshow(mask, cmap = 'grey')
    plot_axis = subsubfigs[1].subplots(1, 1)
    plot_axis.plot(x, y)

plt.savefig('test.png')

This frees the left-hand columns from being tied to the right-hand columns. Note that you will likely prefer some spacing between the subfigures, but presumably you were going to add labels etc.