title: Accessing slice of 3D numpy array
body: <p>I have a 3D numpy array of floating point numbers. Am I indexing the array improperly? I'd like to access slice 124 (index 123) but am seeing this error:</p>
  
  <pre><code>&gt;&gt;&gt; arr.shape
  (31, 285, 286)
  &gt;&gt;&gt; arr[:][123][:]
  Runtime error 
  Traceback (most recent call last):
    File "&lt;string&gt;", line 1, in &lt;module&gt;
  IndexError: index 123 is out of bounds for axis 0 with size 31
  </code></pre>
  
  <p>What would be the cause of this error?</p>