Shade error bar marker without shading error bar line

Question

I'm trying to shade the marker of an errorbar plot, without shading the error bar lines.

Here's a MWE:

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y = [1, 2, 3, 4]
dx = 0.1
dy = 0.1

plt.errorbar(x, y, xerr = dx, yerr = dy, marker = '.', 
             linestyle = ' ', color = 'black', capsize = 2,
             elinewidth = 0.5, capthick = 0.4, alpha = 0.8)

plt.savefig('MWE.pdf')
plt.show()

Also, how do I get rid of the marker edges without changing the capsize? If I put markeredgewidth = 0 the capsize gets reset.

Updated code:

import matplotlib.pyplot as plt
import matplotlib

x = [1, 2, 3, 4]
y = [1, 2, 3, 4]
dx = 0.1
dy = 0.1

other_marker_params = {'marker':'.',
                       'linestyle':' ',
                       'alpha':0.8,
                       'capthick':0.5,
                       'capsize':20,
                       'ecolor':'black',
                       'elinewidth':0.5}

(_, caps, _) = plt.errorbar(x, y, xerr=dx, yerr=dy, markerfacecolor = 'black',
                            markeredgewidth = 0, **other_marker_params)

for cap in caps:
    cap.set_markeredgewidth(1)
    cap.set_markersize(2)

plt.savefig('MWE.pdf')
plt.show()

Answer 1

The second behaviour (markeredgewidth controlling capsize) is strange to me. My guess is because the marker and errorcap lines are both instances of a Line2D object they are both being passed the markeredgewidth parameter you set.

To answer your questions:

• The colour of the marker can be controlled with the kwarg markerfacecolor as follows:

  plt.errorbar(x, y, xerr=dx, yerr=dy, 
               markerfacecolor='red',
               **other_marker_params) # a dict specifying kwargs in
  

• The other issue can be addressed by manually editing the Line2D instances used for the caplines and error bar lines, these are returned by the plt.errorbar function:

  (_, caps, elines) = plt.errorbar(x, y, xerr=dx, yerr=dy, 
                              markerfacecolor='red', 
                              markeredgewidth=0,
                              **other_marker_params)
  
  for cap in caps:
      cap.set_markeredgewidth(1)
      cap.set_markersize(2)
      cap.set_alpha(1)
  for eline in elines:
      eline.set_alpha(1)
  

Using this I can get an image like this:

Reference: I cannot take full credit for the second answer, it is amended from the accepted answer of this SO question.

Edit:

The dictionary other_marker_params may look something like:

other_marker_params = {'marker':'.', 
                       'linestyle':' ', 
                       'ecolor':'black', 
                       'elinewidth':0.5}