title: Merging of two dictionaries
body: <p>I have two dictionaries as follows:</p>
  
  <p><code>D1={'a':1,'b':2,'c':3}</code></p>
  
  <p>and </p>
  
  <p><code>D2={'b':2,'c':3,'d':1}</code></p>
  
  <p>I want to merge these two dictionaries and the result should be as follows:</p>
  
  <p><code>D3={'a':1,'b':2,'c':3,'b':2,'c':3,'d':1}</code></p>
  
  <p>how can I achieve this in python?</p>