title: How are tuples unpacked in for loops?
body: <p>I stumbled across the following code:</p>
  <pre><code>for i, a in enumerate(attributes):
     labels.append(Label(root, text = a, justify = LEFT).grid(sticky = W))
     e = Entry(root)
     e.grid(column=1, row=i)
     entries.append(e)
     entries[i].insert(INSERT,&quot;text to insert&quot;)
  </code></pre>
  <p>I don't understand the <code>i, a</code> bit, and searching for information on <code>for</code> didn't yield any useful results. When I try and experiment with the code I get the error:</p>
  <blockquote>
  <p>ValueError: need more than 1 value to unpack</p>
  </blockquote>
  <p>Does anyone know what it does, or a more specific term associated with it that I can google to learn more?</p>