title: How to count the amount of sub lists in a nested list?
body: <p>I have created a list:</p>
  <pre><code>a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  </code></pre>
  <p>How do I get the count of number of sub-lists in <code>a</code>?
  In this case it is 3.</p>