title: List comprehension as multi-line
body: <p>I am learning Python and trying to understand how to write the list comprehension in the following code as multi-line code. I am just lost as I haven't seen the variable called inside its own comprehension before.</p>
  <pre class="lang-py prettyprint-override"><code>list_of_lists = [['a','b','c','d'],[1,2,3]]
  
  result = [[]]
    for l in list_of_lists:
      result = [x+[y] for x in result for y in l]
  </code></pre>