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I can change the opacity of an item in the legend of a scatter plot

import matplotlib.pyplot as plt

# note the alpha value            vvvvvvvvvv
plt.scatter(range(10), range(10), alpha=0.15, label='Mount Resegone')
plt.scatter(range(10), [0]*10,    alpha=0.15, label='Rimini Beach')
plt.gca().get_legend_handles_labels()[0][0].set_alpha(1.0)
plt.legend()
plt.show()

but doing that I change also the opacity of every dot in the scatter plot.

I guess that there is a single instance of the Patch, correct me if I'm wrong, but my issue is changing the Patch in the legend leaving alone the Patch in the scatter plot.

enter image description here

Addendum

The solution originally suggested (handle._legmarker.set_alpha(1)) does not work in recent Matplotlib, raising an AttributeError

'PathCollection' object has no attribute '_legmarker'

Fortunately it's even easier to have the expected behaviour

plt.scatter(range(10), range(10), alpha=0.15, label='Mount Resegone')
plt.scatter(range(10), [0]*10, alpha=0.15, label='Rimini Beach')
plt.legend().legendHandles[0].set_alpha(1.0)

enter image description here

gboffi
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1 Answers1

2

Edit: You can just do:

leg = plt.legend()
leg.legendHandles[0].set_alpha(1)

Taken from: Set legend symbol opacity

UPDATED: There is an easier way! First, assign your legend to a variable when you >create it:

leg = plt.legend()

Then:

for lh in leg.legendHandles: 
   lh.set_alpha(1)

OR if the above doesn't work (you may be using an older version of matplotlib):

for lh in leg.legendHandles: 
   lh._legmarker.set_alpha(1)

to make your markers opaque for a plt.plot or a plt.scatter, respectively.

Note that using simply lh.set_alpha(1) on a plt.plot will make the lines in your legend opaque rather than the markers. You should be able to adapt these two possibilities for the other plot types.

Nixcc
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  • This work for older Matplotlib's versions, now I have an Attribute Error, `'PathCollection' object has no attribute '_legmarker'` – gboffi Jul 11 '23 at 09:10