Matplotlib, legend with multiple different markers with one label

Question

Here is a simplified plot of the situation:

Instead of have each data point marker have a separate label, I want to be able to have one label for a set of different markers. I would like to be able to have a legend like:

<triangle> <square> <hexagon> <diamond> <circle> Shotcrete strength data points
<green line> 10 minute strength
<blue line> 60 minute strength
<yellow line> 1 day strength
<orange line> 7 day strength
<red line> 28 day strength

I want to do this because in the final plot I will have three sets of data points and showing 18 (3 sets * 6 points/set) marker/label combinations will be messy.

I am using Matplotlib with Python 2.7.

Answer 1

Note: This answer is kept up as a guide to the correct answer - but it does not solve the stated problem. Please see the edit below for the problem of Patch collections not being support in matplotlib.

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One way to go about this, if you want complete customization is to use a so-called Proxy Artist:

from pylab import *

p1 = Rectangle((0, 0), 1, 1, fc="r")
p2 = Circle((0, 0), fc="b")
p3 = plot([10,20],'g--')
legend([p1,p2,p3], ["Red Rectangle","Blue Circle","Green-dash"])

show()

Here you can specify exactly what you'd like the legend to look like, and even use non-standard plot shapes (patches).

Edit: There is some difficulty with this method, matplotlib only supports these Artists in a legend without tweaking. For matplotlib v1.0 and earlier, the supported artists are as follows.

Line2D
Patch
LineCollection
RegularPolyCollection
CircleCollection

Your request of multiple scatter points would be done with a Patch Collection, which is not supported above. In theory with v1.1, this is possible but I do not see how.