title: How to initiate the format of a line in matplotlib?
body: <p>For example,the declaration of a point :
  my_point, = plt.plot([], [], 'bx', alpha=.5).But it comes to wrong,when i use the format like :
  my_line, = plt.plot([,], [,], color='brown', linestyle='-')
  or my_line, = plt.plot([[],[]], [[],[]], color='brown', linestyle='-').
  Because i want to plot a line between two points with data stored in list. I want to get the right format.</p>
  
  <pre><code>my_point, = plt.plot([], [], 'bx', alpha=.5)
  my_line, = plt.plot([,], [,], color='brown', linestyle='-')
  </code></pre>