content: import numpy as np
  import matplotlib.pyplot as plt
  import matplotlib.patches as patches
  x, y = np.random.rand(2, 200)
  
  fig, ax = plt.subplots()
  circ = patches.Circle((0.5, 0.5), 0.25, alpha=0.8, fc='yellow')
  ax.add_patch(circ)
  
  
  ax.plot(x, y, alpha=0.2)
  line, = ax.plot(x, y, alpha=1.0, clip_path=circ)
  
  
  class EventHandler(object):
      def __init__(self):
          fig.canvas.mpl_connect('button_press_event', self.onpress)
          fig.canvas.mpl_connect('button_release_event', self.onrelease)
          fig.canvas.mpl_connect('motion_notify_event', self.onmove)
          self.x0, self.y0 = circ.center
          self.pressevent = None
  
      def onpress(self, event):
          if event.inaxes != ax:
              return
  
          if not circ.contains(event)[0]:
              return
  
          self.pressevent = event
  
      def onrelease(self, event):
          self.pressevent = None
          self.x0, self.y0 = circ.center
  
      def onmove(self, event):
          if self.pressevent is None or event.inaxes != self.pressevent.inaxes:
              return
  
          dx = event.xdata - self.pressevent.xdata
          dy = event.ydata - self.pressevent.ydata
          circ.center = self.x0 + dx, self.y0 + dy
          line.set_clip_path(circ)
          fig.canvas.draw()
  
  handler = EventHandler()
  plt.show()
  