title: Transforming a string in a list
body: <p>How can I transforms strings in list return a list consisting the elements of strings and the lengths of strings? 
  Just like <code>add_sizes([str]) -&gt; [(str, int)]</code> </p>
  
  <p>Here is what I did:</p>
  
  <pre><code>def add_sizes(strings):
      for i in strings:
          return [(i, (len(i)))]
  </code></pre>
  
  <p>but this only works for one string, What should I do if I have more than one string?</p>