title: list.append of an instance of a class function
body: <p>Initialized value of the list ac_hist.  Purpose to keep a historical track of position
      ac_hist = [[450,600]]</p>
  
  <p>This code:</p>
  
  <pre><code>ac_hist.append(aircraft_list[i].get_position()) 
  </code></pre>
  
  <p>should result in a list of lists which represent different [x,y] position.  The value of get_position changes each time it is called. But the results are all the same.  It seems that I'm appending an instance of variable rather than a value and each time the value of the variable changes all of the appended items change value (except the value used to initialize the list)?</p>
  
  <pre><code>print ac_hist 
  </code></pre>
  
  <p>yields the following:</p>
  
  <pre><code>[[450, 600], [1.414, 234.156]]
  [[450, 600], [1.358, 234.552], [1.358, 234.552]]
  [[450, 600], [1.302, 234.948], [1.302, 234.948], [1.302, 234.948]]
  [[450, 600], [1.246, 235.344], [1.246, 235.344], [1.246, 235.344], [1.246,     235.344]]
  </code></pre>