title: pyqtgraph plot does not show up when program executed
body: <p>I am trying to learn how to use pyqtgraph and tried to run the following first simple example given in the above document:</p>
  
  <pre><code>#!/usr/bin/env python3
  
  import pyqtgraph as pg
  
  import numpy as np
  
  x = np.random.normal(size=1000)
  
  y = np.random.normal(size=1000)
  
  pg.plot(x,y,pen=None,symbol='o',title='first graph')
  </code></pre>
  
  <p>I am using python 3.5.3 on a Raspberry Pi 3 with Raspbian Stretch.</p>
  
  <p>If I run the above program in Thonny or IDLE, the program runs without any error but does not display any output.</p>
  
  <p>Similarly, if I run the program at the Linux command prompt by simply calling the program name (I have made it executable using <code>chmod +x</code>) or by typing python3 followed by the program name, still it does not show anything.</p>
  
  <p>However, if I type python3 at the Linux prompt and get a python prompt and then run each of the lines in the program one by one, then it displays a scatter plot in a window titled "first graph" as expected.</p>
  
  <p>Can someone please let me know what I need to do to get the code to display the graph when run through the Thonny or IDLE or by calling it as a program?</p>
  
  <p>Thank you.  </p>