matplotlib - Python: Suplots with two secondary-axis

Question

This is a follow up to this question. I thank maxnoe for the help.

I would like to add a second secondary axis to each of my subplots similarly like in this example but in a subplot.

I tried to set up my figure using:

fig, ((ax1a, ax2a), (ax3a, ax4a)) = host_subplot(4,4, axes_class=AA.Axes)

but I get TypeError: 'AxesHostAxesSubplot' object is not iterable and

ValueError: Illegal argument(s) to subplot: (4, 4)

Is it possible to have a subplot where each figure has two secondary axes?

Answer 1

plt.subplots is a convenience function for creating the figure and multiple subplots at once. However, its powers are limited. If you want to create special axes, you will have to initialize them the 'hard' way.

Adapting the example you mentioned for a grid of 2x2 subplots with the shown properties. To avoid to much repetetive code, i'm using a for loop to initialize all the plots and store them in a list of dictionaries.

from mpl_toolkits.axes_grid1 import host_subplot
import mpl_toolkits.axisartist as AA
import matplotlib.pyplot as plt

subplots = []
rows = 2
columns = 2

for n in range(rows * columns):
    host = host_subplot(rows, columns, n + 1, axes_class=AA.Axes)

    par1 = host.twinx()
    par2 = host.twinx()

    offset = 60

    par2.axis["right"] = par2.get_grid_helper().new_fixed_axis(
        loc="right",
        axes=par2,
        offset=(offset, 0),
    )

    par2.axis["right"].toggle(all=True)

    host.set_xlabel("Distance")
    host.set_ylabel("Density")
    par1.set_ylabel("Temperature")
    par2.set_ylabel("Velocity")

    subplots.append({
        'density': host,
        'temperature': par1,
        'velocity': par2,
    })


subplots[0]['density'].plot([1, 2, 3])
subplots[2]['temperature'].plot([1, 2, 3])
plt.tight_layout()
plt.savefig('result2.png', dpi=300)

Result: