title: python slicing multi levels list of dict using list comprehension
body: <p>I have 3 lvls deep list as follows: </p>
  
  <pre><code>parent = [
     [
        {'x': 1, 'y': 2},
        {'x': 3, 'y': 8},
        .
        .
        .
     ],
     [
        {'x': 8, 'y': 5},
        {'x': 9, 'y': 6},
        .
        .
        .
     ]
  ]
  </code></pre>
  
  <p>I am trying to use list comprehension to get all the x into a list and all the y into another list</p>
  
  <p>I tried something like this: 
  [gc for gc in [c for c in [p.get('x') for p in parent]]] </p>
  
  <p>but the get('x') is still hitting a list instead of an element, mainly because of the most inner [].  Any idea how to achieve this?</p>