title: Python nested dictionary comprehension returns empty dictionaries
body: <p>I'm using dictionary comprehension to pull out a nested value. I have the following code (as a sample):</p>
  
  <pre><code>d = {1: 'a', 2: 'b', 3: 'c'}
  e = {4: 'd', 5: 'e', 6: 'f'}
  f = {7: 'g', 8: 'h', 9: 'i'}
  
  # stick them together into another dict
  data_dict = {'one': d, 'two': e, 'three': f}
  #say we're looking for the key 8
  
  output = {outer_key: {inner_key: inner_value for inner_key, inner_value in outer_value.items() if inner_key == 8} for outer_key, outer_value in data_dict.items()}
  output = {'one': {}, 'three': {8: 'h'}, 'two': {}}
  </code></pre>
  
  <p>what do I need to do to get JUST 'three' and its value? I don't want to return empty matches. </p>
  
  <p>thx</p>