How to add a legend to a scatter plot in matplotlib ?

Examples of how to add a legend to a scatter plot in matplotlib:

Add a simple legend to a scatter plot

Using the pyplot function legend():

import matplotlib.pyplot as plt

x = [1,2,3,4]
y = [4,1,3,6]

plt.scatter(x, y, c='coral', label='Class 1')

x = [5,6,7,8]
y = [1,3,5,2]

plt.scatter(x, y, c='lightblue', label='Class 2')

plt.legend()

plt.title('Nuage de points avec Matplotlib')
plt.xlabel('x')
plt.ylabel('y')

plt.savefig('ScatterPlot_09.png')
plt.show()

Add a legend to a scatter plot using "Proxy artists"

Another example using Proxy artists):

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
import numpy as np

x = [1,2,3,4,5,6,7,8]
y = [4,1,3,6,1,3,5,2]

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

colormap = np.array(['#0b559f', '#89bedc'])

plt.scatter(x, y, s=100, c=colormap[categories])

pop_a = mpatches.Patch(color='#0b559f', label='Population A')
pop_b = mpatches.Patch(color='#89bedc', label='Population B')

plt.legend(handles=[pop_a,pop_b])

plt.title('Nuage de points avec Matplotlib')
plt.xlabel('x')
plt.ylabel('y')

plt.savefig('ScatterPlot_10.png')
plt.show()

References