How to insert a figure (3x3 subplot) into a subplot in matplotlib python

Question

I want to insert a 3x3 figure into a subplot. Here and here is shown a similar problem, but the solution seems not to work in case (I think).

Can anyone please provide some code (as simple as possible) in order to produce this:

I'd be glad if someone could help with that, thanks in advance. Any answer or comment would be appreciated.

Answer 1

I created a workaround solution using this answer. The part added by me is written below the line with a comment #. I admit this is not general and perfect, but still sufficient in my opinion to get the work done.

import matplotlib.pyplot as plt
import numpy as np

def add_subplot_axes(ax, rect): # This is the function in the linked answer
    fig = plt.gcf()
    box = ax.get_position()
    width = box.width
    height = box.height
    inax_position  = ax.transAxes.transform(rect[0:2])
    transFigure = fig.transFigure.inverted()
    infig_position = transFigure.transform(inax_position)    
    x = infig_position[0]
    y = infig_position[1]
    width *= rect[2]
    height *= rect[3]  
    subax = fig.add_axes([x,y,width,height])
    x_labelsize = subax.get_xticklabels()[0].get_size()
    y_labelsize = subax.get_yticklabels()[0].get_size()
    x_labelsize *= rect[2]**0.5
    y_labelsize *= rect[3]**0.5
    subax.xaxis.set_tick_params(labelsize=x_labelsize)
    subax.yaxis.set_tick_params(labelsize=y_labelsize)
    return subax

# Modified part below

fig = plt.figure(figsize=(8,6))
ax = fig.add_subplot(111)
x_start, y_start = 0.4, 0.4
for i in range(3):
    for j in range(3):
        rect = [x_start+0.2*i, y_start+0.2*j, 0.15, 0.15]
        ax_ = add_subplot_axes(ax,rect)
        ax_.tick_params(labelsize=6)
plt.show()