title: python nested list comprehension string concatenation
body: <p>I have a list of lists in python looking like this:</p>
  
  <pre><code>[['a', 'b'], ['c', 'd']]
  </code></pre>
  
  <p>I want to come up with a string like this:</p>
  
  <pre><code>a,b;c,d
  </code></pre>
  
  <p>So the lists should be separated with a <code>;</code> and the values of the same list should be separated with a <code>,</code></p>
  
  <p>So far I tried <code>','.join([y for x in test for y in x])</code> which returns <code>a,b,c,d</code>. Not quite there, yet, as you can see.</p>