title: Why can't I append 2 dimension list vertically? The last list effects all element
body: <p>I am coding by using <strong>python</strong>. I just want to append this two lists. So, I want to make this(below current). these variables( past, curent) are not constant. I mean that their size are changeable. And, according to their size, the number of iteration is also changeable.</p>
  
  <p>First iteration</p>
  
  <p>past(1)=</p>
  
  <pre><code>[[0, 0, 0, 1], [0, 1, 0, 1], [1, 0, 0, 1], [1, 1, 0, 1]]
  </code></pre>
  
  <p>Second iteration</p>
  
  <p>past(2)=</p>
  
  <pre><code>[[0, 0, 1, 1], [0, 1, 1, 1], [1, 0, 1, 1], [1, 1, 1, 1]]
  </code></pre>
  
  <p>(I want to make this) </p>
  
  <p>curent=</p>
  
  <pre><code>[[0, 0, 0, 1], 
  [0, 1, 0, 1], 
  [1, 0, 0, 1], 
  [1, 1, 0, 1],
  [0, 0, 1, 1], 
  [0, 1, 1, 1], 
  [1, 0, 1, 1], 
  [1, 1, 1, 1]]
  </code></pre>
  
  <p>I wrote "current.append(past)"
  Because of "<strong>call by reference</strong>", 
  current variable was below my variable</p>
  
  <p>Error</p>
  
  <pre><code>[[0, 0, 1, 1], 
  [0, 1, 1, 1], 
  [1, 0, 1, 1], 
  [1, 1, 1, 1],
  [0, 0, 1, 1], 
  [0, 1, 1, 1], 
  [1, 0, 1, 1], 
  [1, 1, 1, 1]]
  </code></pre>
  
  <p>How can I prevent call by reference?
  Simply speaking, I just want [past1, past2, past3,...].
  But,  because of call by reference, I made [lastPast, lastPast, lastPast,...]
  I cannot use numpy.
  As you can see, I just want append 2 dimension list vertically.</p>