title: How to check if a python dictionary keys has same value(s) and extract those value(s)
body: <p>I would like to know how to extract values in a dictionary that appear for all keys.</p>
  
  <p>So for instance, if i have the following dictionary:</p>
  
  <pre><code>d = {'a': [num_1, num_2], 'b': [num_1],
                  'c': [num_1,num_2, num_3]}
  </code></pre>
  
  <p>I would like to extract the value which exists for all keys, in this instance num_1.</p>
  
  <p>How can i achieve this?</p>
  
  <p><strong>EDIT:</strong> how would i store the common value(s) in a list?</p>