title: Add values in two dictionaries together on same key
body: <p>How can I approach adding items from two table-indexed dictionaries together as in this simple example?</p>
  
  <pre><code>table1 = {'item1': {'quantity': 3, 'value': 3.0}, \
            'item2': {'quantity': 10, 'value': 30} \
            }
  
  table2 = {'item1': {'quantity': 5, 'value': 5.0}, \
            'item3': {'quantity': 7, 'value': 10.5} \
            }
  
  newDic = {'item1': {'quantity': 8, 'value': 8.0}, \
            'item2': {'quantity': 10, 'value': 30}, \
            'item3': {'quantity': 7, 'value': 10.5} \
            }
  </code></pre>
  
  <p>I have a function that parses and filters contents of a flat file into a dictionary. I'd like to redesign the script to parse multiple files. Each table has exactly the same column headers. The rows have same items with different values, but some files have <em>additional</em> items.</p>