Having just one legend when using matplotlib zoomed_inset_axes

Question

I'd like to make a fairly straight forward plot with 4 sets of data, two in the main plot, and two in the insert (on a different scale).

This is the starting code::

w1snr_limit = np.arange(0, 50, 0.5)
w2snr_limit = np.arange(0, 50, 0.5)
w3snr_limit = np.arange(0, 10, 0.5)
w4snr_limit = np.arange(0, 10, 0.5)

w1snr_percent = w1snr_limit**(1/2.)
w2snr_percent = w2snr_limit**(1/2.)
w3snr_percent = w3snr_limit**(1/3.)
w4snr_percent = w4snr_limit**(1/4.)

fig, ax = plt.subplots(figsize=(8.0, 8.0))
xmin =   0.00 
xmax =  50.00
ymin =   0.00  
ymax = 100.00

ax.scatter(w1snr_limit, w1snr_percent, s=ms, alpha=0.85, label='W1 SNR')
ax.scatter(w2snr_limit, w2snr_percent, s=ms, alpha=0.85, label='W2 SNR')

ax.set_xlim((xmin, xmax))
ax.set_ylim((ymin, ymax))

Then there would be this inset plot::

axins = zoomed_inset_axes(ax, 2.0,  loc='lower right')
# sub region of the original image
x1, x2, y1, y2 = 0.0, 10., 0.0, 20.0
axins.set_xlim(x1, x2)
axins.set_ylim(y1, y2)
axins.scatter(w3snr_limit, w3snr_percent, s=ms, alpha=0.85, label='W3 SNR', color='green')
axins.scatter(w4snr_limit, w4snr_percent, s=ms, alpha=0.85, label='W4 SNR', color='red')

But then I first struggle to get the inset plot properly placed (ie the two x-axes are all munched up) and also it's unclear to me how you get all 4 datasets into the same legend

handles, labels = ax.get_legend_handles_labels()

handles = [handles[0], handles[1], handles[2], handles[3]]
labels = [labels[0], labels[1], labels[2],labels[3]]

ax.legend(handles,labels,loc=2)

leads to a

IndexError: list index out of range

error. Little help just to get these things sorted?

Answer 1

1. Not sure what "properly placed" means, but since the data is in the lower part of the figure, I'd suggest to use "upper right" as loc .
2. You need to supply the handles and labels of both the ax and the axins to the legend to have them all in the legend.

Complete example:

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1.inset_locator import zoomed_inset_axes

w1snr_limit = w2snr_limit = np.arange(0, 50, 0.5)
w3snr_limit = w4snr_limit = np.arange(0, 10, 0.5)

w1snr_percent = w1snr_limit**(1/2.)
w2snr_percent = w2snr_limit**(1/2.)
w3snr_percent = w3snr_limit**(1/3.)
w4snr_percent = w4snr_limit**(1/4.)

fig, ax = plt.subplots(figsize=(8.0, 8.0))
xmin, xmax = 0., 50.
ymin, ymax = 0., 100. 

ax.scatter(w1snr_limit, w1snr_percent, s=6, alpha=0.85, label='W1 SNR')
ax.scatter(w2snr_limit, w2snr_percent, s=6, alpha=0.85, label='W2 SNR')

ax.set_xlim((xmin, xmax))
ax.set_ylim((ymin, ymax))

axins = zoomed_inset_axes(ax, 2.0,  loc='upper right')
# sub region of the original image
x1, x2, y1, y2 = 0.0, 10., 0.0, 20.0
axins.set_xlim(x1, x2)
axins.set_ylim(y1, y2)
axins.scatter(w3snr_limit, w3snr_percent, s=6, alpha=0.85, label='W3 SNR', color='green')
axins.scatter(w4snr_limit, w4snr_percent, s=6, alpha=0.85, label='W4 SNR', color='red')

handles, labels = ax.get_legend_handles_labels()
handles1, labels1 = axins.get_legend_handles_labels()

ax.legend(handles+handles1, labels+labels1, loc=2)

plt.show()