creating a matplotlib scatter legend size related

Question

I am looking for a way to include a (matplotlib) legend that describe the size of points in a scatter plot, as this could be related to another variable, like in this basic

Answer 1

Building on mjp's and jpobst's answers, if you have more than two discrete sizes you can make a loop and include the labels in the call to plt.scatter():

msizes = [3, 4, 5, 6, 7]
markers = []
for size in msizes:
   markers.append(plt.scatter([],[], s=size, label=size))

plt.legend(handles=markers)

Note that you can format the label using standard string formatting, such as label = ('M%d' %size) for the labels in mjp's answer.