Matplotlib Errorbar Caps Missing

What worked for me was adding this (as per: How to set the line width of error bar caps, in matplotlib):

(_, caps, _) = plt.errorbar(x,y, yerr=err, capsize=20, elinewidth=3)

for cap in caps:
    cap.set_color('red')
    cap.set_markeredgewidth(10)

Slight simplification of astromax's answer:

plt.errorbar(x,y, yerr=err, capsize=20, elinewidth=3, markeredgewidth=10)

It seems that somehow markeredgewidth is defaulting to 0 sometimes.

It has to do with the rcParams in matplotlib. To solve it, add the following lines at the beginning of your script:

import matplotlib
matplotlib.rcParams.update({'errorbar.capsize': 2})

It also works with plt.bar().

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