title: Create a dictionary using key sets
body: <p>I have 2 dictionary:</p>
  
  <pre><code>a = {'a':5, 'b':3, 'c':1}
  b = {"ca":10, "sd":4, "aa":2}
  </code></pre>
  
  <p>What I want to obtain is:</p>
  
  <pre><code>z = {'a':"ca", 'b':"sd", 'c':"aa"}
  </code></pre>
  
  <p>How can I do this?</p>
  
  <p>Edit:</p>
  
  <p>I want to match the 1st key of a with the 1st key of b, the 2nd of a with the 2nd of b and so on.</p>