title: x, = ... - is this trailing comma the comma operator?
body: <p>I don't understand what does comma after variable <strong>lines,</strong> means: <a href="http://matplotlib.org/examples/animation/simple_anim.html" rel="noreferrer">http://matplotlib.org/examples/animation/simple_anim.html</a></p>
  
  <pre><code>line, = ax.plot(x, np.sin(x))
  </code></pre>
  
  <p>If I remove comma and variable "line," becomes variable "line" then program is broken. Full code from url given above:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  import matplotlib.animation as animation
  
  fig = plt.figure()
  ax = fig.add_subplot(111)
  
  x = np.arange(0, 2*np.pi, 0.01)        # x-array
  line, = ax.plot(x, np.sin(x))
  
  def animate(i):
      line.set_ydata(np.sin(x+i/10.0))  # update the data
      return line,
  
  #Init only required for blitting to give a clean slate.
  def init():
      line.set_ydata(np.ma.array(x, mask=True))
      return line,
  
  ani = animation.FuncAnimation(fig, animate, np.arange(1, 200), init_func=init,
      interval=25, blit=True)
  plt.show()
  </code></pre>
  
  <p>According to <a href="http://docs.python.org/3/tutorial/datastructures.html#tuples-and-sequences" rel="noreferrer">http://docs.python.org/3/tutorial/datastructures.html#tuples-and-sequences</a> comma after variable seems to be related to tuples containing only one item.</p>