title: Iterate a list of tuples
body: <p>I'm looking for a clean way to iterate over a list of tuples where each is a pair like so <code>[(a, b), (c,d) ...]</code>. On top of that I would like to alter the tuples in the list.</p>
  
  <p>Standard practice is to avoid changing a list while also iterating through it, so what should I do? Here's what I kind of want:</p>
  
  <pre><code>for i in range(len(tuple_list)):
    a, b = tuple_list[i]
    # update b's data
    # update tuple_list[i] to be (a, newB)
  </code></pre>