title: how to add to a dictionary value or create if not exists
body: <p>I want to add to a value in a dictionary storing counters:</p>
  
  <pre><code>d[key] += 1
  </code></pre>
  
  <p>but sometimes the key will not exist yet. Checking to see if the key exists seems too ugly. Is there a nice and pythonic one liner for this - add if the key exists, or create the value <code>1</code> if the key is not in the dict.keys ?</p>
  
  <p>thanks</p>