Question

A simple plot with a legend made with matplotlib produces the following: the markers at the left of the labels of my legend appear twice. Can anyone know why and how to avoid the problem? My command is:

pl.plot(x1,x2,'g^', label='regional')
pl.plot(y1,y2,'bo', label='local')
pl.legend( loc='upper left' )

Thank you

Answer 1

You can change the number of markers shown in the legend by using the numpoints keyword:

import matplotlib.pyplot as plt
import numpy as np
x1 = y1 = np.linspace(0, 10, 100)
x2 = np.sin(x1)
y2 = np.cos(y1)
plt.plot(x1,x2,'g--^', label='regional')
plt.plot(y1,y2,'b-o', label='local')
plt.legend( loc='upper left', numpoints = 1 )
plt.show()

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I believe the reason the markers appear twice (by default) is because matplotlib is trying to show the linestyle connectors between the markers. It looks a little odd when there is no connector.

If the plot had solid and dashed lines,

plt.plot(x1,x2,'g--^', label='regional')
plt.plot(y1,y2,'b-o', label='local')

then the legend looks like this:

and now you can see the effect of the linestyle between the markers in the legend (as well as on the graph).

---

If you don’t want any legend handle at all, then you could use

plt.legend(..., handlelength=0)

For example,

import numpy as np
import matplotlib.pyplot as plt

x1 = y1 = np.linspace(0, 10, 100)
x2 = np.sin(x1)
y2 = np.cos(y1)
plt.plot(x1,x2,'g--^', label='regional')
plt.plot(y1,y2,'b-o', label='local')
plt.legend(loc='best', numpoints=1, handlelength=0)
plt.show()

You could use

plt.legend(loc='best', numpoints=1, handlelength=0, 
           markerscale=0, handletextpad=0)

to remove the legend marker as well.