title: How to handle multiple keys for a dictionary in python?
body: <p>I've been searching about how to go for adding multiple val for single keys in a Dict if a duplicate key is found.</p>
  
  <p>Let's take an example:</p>
  
  <pre><code>list_1 = ['4', '6' ,'8', '8']
  list_2 = ['a', 'b', 'c', 'd']
  new_dict = dict(zip(list_1,list_2))
  ...output...
  {'8': 'd', '4': 'a', '6': 'b'}
  </code></pre>
  
  <p>Expected output :</p>
  
  <pre><code>{'8': 'c,d', '4': 'a', '6': 'b'}
  </code></pre>
  
  <p>In order to process the above two list and combine them into one dict, i would face a certain challenge that we can't have two 8's in the 'key' of dict, which is a default behavior and i understand why !! </p>
  
  <p>Some of the options that exists to process such scenario are :</p>
  
  <p>1) Find if 'key' already exists in dict, if yes, then append the new val to 'key'</p>
  
  <p>2) Create a mutable object to reference each key and in that way you can have multiple dup keys ~~Not really my use case</p>
  
  <p>So, how can i go about for expected output using option#1 ?</p>