title: Python find list lengths in a sublist
body: <p>I am trying to find out how to get the length of every list that is held within a particular list. For example:</p>
  
  <pre><code>a = []
  a.append([])
  a[0].append([1,2,3,4,5])
  a[0].append([1,2,3,4])
  a[0].append([1,2,3])
  </code></pre>
  
  <p>I'd like to run a command like: </p>
  
  <pre><code>len(a[0][:]) 
  </code></pre>
  
  <p>which would output the answer I want which is a list of the lengths [5,4,3]. That command obviously does not work, and neither do a few others that I've tried. Please help!</p>