在图例中绘制代表性的误差线大小？

Question

I have some data (with errors) to be plotted in a rather dense display. I would like to plot these points without errorbars (because it makes it too busy), but to plot a representative error bar in a legend (which shows the errorbar with an accurate size).

Here is what I have so far (which is not successful).

import pylab as pl
p1, = pl.plot([1,2,3], label="test1")
p2, = pl.plot([3,2,1], label="test2")

errorbarsize = 1.65 # Need this to be properly scaled in the legend

# p3, = pl.plot([1], label='data', color="red") # works
# p3, = pl.scatter(1, 1, label='data', color="red")
# p3, = pl.errorbar(1, 1, yerr=errorbarsize, label='data', color="red")

l1 = pl.legend([p1], ["Label 1"], loc=1)
l2 = pl.legend([p2], ["Label 2"], loc=2) # this removes l1 from the axes.
l3 = pl.legend([p3], ["Label 3"], loc=3, numpoints=1)

gca().add_artist(l1) # add l1 as a separate artist to the axes
gca().add_artist(l2) # add l2 as a separate artist to the axes

Also, it would be best if I could plot this in a separate legend, but that might be asking too much.

Answer 1

Here is an example using Thorsten Kranz's suggestion, and another example of how to show representative error bars...

import matplotlib.pyplot as plt
import numpy as np

fig, axs = plt.subplots(2,1)

# -- make some fake data
x = np.random.normal(loc=4, size=100)
x.sort()
y = np.random.normal(loc=5, size=100)
y.sort()
y_errorbarsize = y.std()
x_errorbarsize = y.std()

### Example 1
# From Thorsten Kranz comment...
axs[0].plot(x, y, label="Example #1")

axs[0].fill_between(x,y-y_errorbarsize/2, y+y_errorbarsize/2,alpha=0.3)

### Example 2

axs[1].scatter(x, y, label="Example #2", alpha=0.8)

# Place our representative error bar by hand.
axis_coordinates_of_representative_error_bar = (0.1, 0.8)
screen_coordinates_of_representative_error_bar = axs[1].transAxes.transform(axis_coordinates_of_representative_error_bar)
screen_to_data_transform = axs[1].transData.inverted().transform
data_coordinates_of_representative_error_bar = screen_to_data_transform(screen_coordinates_of_representative_error_bar)
foo = data_coordinates_of_representative_error_bar

axs[1].errorbar(foo[0], foo[1], xerr=x_errorbarsize/2, yerr=y_errorbarsize/2, capsize=3)

plt.show()
plt.close()