title: Building a 3D array from a number of 2D arrays with numpy
body: <p>Let's start with 2 2D arrays:</p>
  
  <pre><code>import numpy as np
  a = np.zeros( (3,4) )
  b = np.zeros( (3,4) )
  </code></pre>
  
  <p>Now let's combine them into a 3D array:</p>
  
  <pre><code>c = np.stack( (a,b) )
  </code></pre>
  
  <p>Everything fine so far, but how to add an additional 2D array to the 3D array, the following is not working:</p>
  
  <pre><code>np.stack( (c,a) )
  </code></pre>
  
  <p>So, my question is how to add an additional layer to the 3D array? (numpy version <code>1.12.1</code>)</p>