matplotlib legend circle markers

Question

I'm making a legend for a scatter plot using a proxy artists (http://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist) and attempting to make circle-shaped markers.

This is my code:

legend([Circle((0,0), fc='g')], ["Green Circle"])

But when I plot it, the legend doesn't have a circle and instead displays a rectangle...

How do I get the legend to have circle markers?

Answer 1

If all you are looking for is a circular marker in the legend (as opposed to strictly using proxy artists), then I suggest trying something like:

line1 = Line2D([], [], color="white", marker='o', markerfacecolor="red")
line2 = Line2D([], [], color="white", marker='o', markerfacecolor="green")
line3 = Line2D([], [], color="white", marker='o', markersize=5,  markerfacecolor="slategray")
line4 = Line2D([], [], color="white", marker='o', markersize=10, markerfacecolor="slategray")
plt.legend((line1, line2, line3, line4), ('Thing 1', 'Thing 2', 'Thing 3', 'Thing 4'), numpoints=1, loc=1)

This shows you circles of different color and sizes, where the 2D line that is drawn is white (hence color="white"). If you don't want the circles filled in, for example, set markeredgecolor="green" and markerfacecolor="white".

Further tweaks

• If you don't have a white background, or if the line intersects with the grid in the background, color="white" will still show the line. linewidth=0 will completely hide the line.
• Use the handletextpad keyword argument for plt.legend to reduce the space between the circle and the label. The value can also be negative, e.g. handletextpad=-0.3.
• If you are using seaborn palettes, you can set the individual marker face colors by indexing the palette. E.g. markerfacecolor=sns.color_palette("cubehelix", 3)[0]

Answer 2

@punkkat When adding patches (which Circle is) to be added to a legend, it is not the patch itself which is added, but a new Rectangle patch is created with exactly the same properties (color, hatching, alpha etc.) of the given patch. Hence, no matter the incoming shape, the result will be a square patch in the legend.

The simple solution, as given by @cosmosis, is to pass line instances to legend, which can support arbitrary markers, and since there is no limitation on the shape of a marker, there is no limitation on the shapes that you can pass to be put on the legend.