title: Google App Engine - Request class query_string
body: <p>In Python and GAE, I would like to ask how to get the parameters of a query string in the url. 
  As I know, the  query_string part returns all the part after the "?" in the url. So what I have to do is to split the query string with "&amp;", and use the variables.
  Is there any other convinient way to manage the query string?
  How do you normally do it? </p>
  
  <pre><code>str_query = self.request.query_string
  m = str_query.split('&amp;')
  a = m[0] 
  b = m[1]
  c = m[2]
  </code></pre>
  
  <p>Doing this way, in case, the query_string does not have any values, it threw an error:</p>
  
  <pre><code>IndexError: list index out of range
  </code></pre>