title: boto dynamodb conditional projectionexpression in query/scan alternative
body: <p>I am a beginner in Python.
  I am trying to fetch query and scan results from dynamodb. As per the syntax, I am able to fetch the results using </p>
  
  <pre><code>        response = table.get_item(
              Key={
                  pk_key: pk_value,
              },
              ExpressionAttributeNames={'#key_1': 'key_1'},
              ProjectionExpression='#key_1'
          )
  </code></pre>
  
  <p>But I need to reuse my code so as to handle situations where ProjectionExpression/ExpressionAttributeNames is not required. Please suggest if I can handle this apart from writing an overloaded function for each different scenario as in that case number of functions will shoot up.</p>