title: TypeError: unsupported operand type(s) for +: 'set' and 'set'
body: <p>I'm trying to learn python for data science application and signed up for a course. I am doing the exercises and got stuck even though my answer is the same as the one in the answer key.</p>
  <p>I'm basically trying to add two new items to a dictionary with the following piece of code:</p>
  <pre><code># Create a new key-value pair for 'Inner London'
  location_dict['Inner London'] = location_dict['Camden'] + location_dict['Southwark']
  
  # Create a new key-value pair for 'Outer London'
  location_dict['Outer London'] = location_dict['Brent'] + location_dict['Redbridge']
  </code></pre>
  <p>but when I run it I am getting a <code>TypeError</code>.</p>