title: `if key in dict` vs. `try/except` - which is more readable idiom?
body: <p>I have a question about idioms and readability, and there seems to be a clash of Python philosophies for this particular case:</p>
  
  <p>I want to build dictionary A from dictionary B. If a specific key does not exist in B, then do nothing and continue on.</p>
  
  <p>Which way is better?</p>
  
  <pre><code>try:
      A["blah"] = B["blah"]
  except KeyError:
      pass
  </code></pre>
  
  <p>or </p>
  
  <pre><code>if "blah" in B:
      A["blah"] = B["blah"]
  </code></pre>
  
  <p>"Do and ask for forgiveness" vs. "simplicity and explicitness".</p>
  
  <p>Which is better and why?</p>