matplotlib can not see the effect of setting edgecolor in plt.savefig() or plt.figure()

Question

I can't figure out how to add a border around a figure, it's my understanding that this would be the figure.edgecolor parameter or savefig(edgecolor) but this does not appear to work. I'm using matplotlib 1.1.1. I would expect this code to draw a red border around the figure:

import matplotlib.pyplot as plt
plt.plot([1,2,3])
plt.savefig('test.png', edgecolor='r', facecolor='g')

When I look at the figure it has a green facecolor, but I don't see a red edgecolor?

The following doesn't work either:

import matplotlib.pyplot as plt
plt.figure(edgecolor='r', facecolor='g')
plt.plot([1,2,3])
plt.show()

Again I see the green facecolor, but no red edgecolor. What am I doing wrong?

Any ideas?

Answer 1

According to the documentation of matplotlib.figure.Figure(), the figure's edge linewidth is set to 0.0 by default. You can visualize the edgecolor if you bump up this value in either of your code snippets:

import matplotlib.pyplot as plt
plt.figure(linewidth=2)
plt.plot([1,2,3])
plt.savefig('test.png', edgecolor='r', facecolor='g')

Or:

import matplotlib.pyplot as plt
plt.figure(edgecolor='r', facecolor='g', linewidth=2)
plt.plot([1,2,3])
plt.show()

linewidth=0.0 is a good default, but it should be better documented in matplotlib.pyplot.savefig().