title: Merge two dictionaries and keep the values for duplicate keys in Python
body: <p>Let's suppose that I have two dictionaries: </p>
  
  <pre><code>dic1 =  { "first":1, "second":4, "third":8} 
  dic2 =  { "first":9, "second":5, "fourth":3}
  </code></pre>
  
  <p>Is there a straightforward way to obtain something like the below? </p>
  
  <pre><code>dic3 =  { "first":[1,9], "second":[4,5], "third":[8], "fourth":[3]}
  </code></pre>
  
  <p>I used lists to store values, but tuples are fine as well.</p>