title: Why matplotlib give the error [<matplotlib.lines.Line2D at 0x111fa5588>]?
body: <p>I'm programming in python and I work on OS Yosemite with Anaconda: Conda Version: 3.15.1, Python Version: 3.4.3.final.0 and I have this problem with plot: </p>
  
  <pre><code>import matplotlib.pyplot as plt   
  a=[1,2,3] 
  b=[10,20,30]
  plt.plot(a,b)
  plt.show()
  </code></pre>
  
  <p>but I have the error: []. I read some other question about the same problem but I have not resolved my problem.
  Thanks in advance.
  Giuseppe</p>