title: split a string into a list of tuples
body: <p>If i have a string like:</p>
  
  <pre><code>"user1:type1,user2:type2,user3:type3" 
  </code></pre>
  
  <p>and I want to convert this to a list of tuples like so:</p>
  
  <pre><code>[('user1','type1'),('user2','type2'),('user3','type3')]
  </code></pre>
  
  <p>how would i go about doing this?  I'm fairly new to python but couldn't find a good example in the documentation to do this.</p>
  
  <p>Thanks!</p>