title: Loop over 2 lists, repeating the shortest until end of longest
body: <p>I am sure there is an easy and obvious way to do this, but I have been googling and reading the docs and I just cannot find anything.</p>
  
  <p>This is what I want to achieve:</p>
  
  <pre><code>la = ['a1', 'a2', 'a3', 'a4']
  lb = ['b1', 'b2']
  result = ['a1_b1', 'a2_b2', 'a3_b1', 'a4_b2']
  </code></pre>
  
  <p>I have a list of dates and some of them have something marked on them. I then have a much larger list of dates and I want to put the smallest list inside the bigger list as many times as possible. It will probably require some sort of loop as I need access to the dates in the larger list for the end result.</p>
  
  <p>For some reason, I just cannot see a good way to do this.</p>