title: How to unfold a python dictionary with lists as values into a list of key-value tuples with two elements?
body: <p>I have this kind of dictionary:</p>
  
  <pre><code>{'a': [1, 2], 'b': [4, 5, 6]}
  </code></pre>
  
  <p>I'd like to know how to unfold it into a list of tuples like so:</p>
  
  <pre><code>[('a', 1), ('a', 2), ('b', 4), ('b', 5), ('b', 6)]
  </code></pre>
  
  <p>What is the best way to achieve this in Python 3?</p>