title: Why can't I add a single Ellipse (patch) to more than one axis?
body: <p>Why do I need a new instance of a patch for each axis I'm going to add it to? When does the patch depend on an axis, and why can't the mathematical definition be added to different axes to be drawn more than once? Is the <code>oneEllipse</code> the efficient way to deal with this? </p>
  
  <p>If the Ellipse is an artist on the current axis (if otherwise unspecified), why can I add <code>f, g</code> below to different axes when they were created with the same current axis? </p>
  
  <pre><code>import numpy as np
  import  matplotlib.pyplot as plt
  from matplotlib.patches import Ellipse
  
  x, y, width, height, angle=10.0, 6.0, 7.0, 3.0, 160.0
  
  fig = plt.figure(figsize=(12,8))
  ax1 = fig.add_subplot(121)
  ax2 = fig.add_subplot(122)
  
  def oneEllipse():
      return Ellipse(xy=(x,y), width=height, height=width, angle=angle,
              facecolor='blue')
  
  e = Ellipse(xy=(x,y), width=width, height=height, angle=angle,
              facecolor='black')
  
  f = Ellipse(xy=(x+2,y+2), width=width, height=height, angle=angle,
              facecolor='green')
  g = Ellipse(xy=(x+2,y+2), width=width, height=height, angle=angle,
              facecolor='green')
  
  
  #ax1.add_artist(e) # Can use e only once --
  ax2.add_artist(e) # if added twice, appears on neither axis
                    # whether called in loop or not
  
  ax1.add_artist(f) # These were defined with the same gca(), weren't they?
  ax2.add_artist(g) # Why not the same behavior as e?
  
  for ax in (ax1, ax2):
      ax.set_aspect('equal')
      ax.set(xlim=(0,20), ylim=(0,10))
      ax.add_artist(oneEllipse()) # Generating a new Ellipse each time, fine
      ax.add_artist(e) # if e was added to the last axis in the loop *only*,
                       # it appears if in loop
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/WI91E.png" alt="enter image description here"></p>
  
  <p>Edited to add: duplicate of <a href="https://stackoverflow.com/questions/21638546/adding-the-same-patch-instance-to-multiple-subplots-in-matplotlib">Adding the same Patch instance to multiple subplots in matplotlib</a> but with more examples of what fails how. </p>