title: line, = ax.plot(x,y)
body: <p>I want to know the meaning of the <strong>&quot;,&quot;</strong> after <strong>&quot;line&quot;</strong>.</p>
  <pre><code>line, = ax.plot(rand(100), rand(100), 'o', picker=line_picker)
  </code></pre>
  <p>It seems important to the code.
  Without the &quot;,&quot; my code crushed.
  The error is &quot;AttributeError: 'list' object has no attribute 'get_xdata'&quot;</p>
  <pre><code>from matplotlib import pyplot as plt
  import numpy as np
  
  class PointBuilder:
      def __init__(self, line):
          self.line = line
          self.xs = list(line.get_xdata())
          self.ys = list(line.get_ydata())
          self.cid = line.figure.canvas.mpl_connect('pick_event', self)
  
      def __call__(self, event):
          print('click', event)
          ind = event.ind[0]
          self.xs.remove(self.xs[ind])
          self.ys.remove(self.ys[ind])
          self.line.set_data(self.xs, self.ys)
          self.line.figure.canvas.draw()
  
  fig = plt.figure()
  ax = fig.add_subplot(111)
  ax.set_title('click to build line segments')
  line = ax.plot(demag_data[&quot;X corr&quot;], demag_data['Y corr']*-1, 'o',color='tab:blue', picker=5)
  linebuilder = PointBuilder(line)
  
  plt.show()
  </code></pre>