title: Extracting first elements from a list of tuples using list comprehension
body: <p>I have a list of tuples of which I want to extract the first element of each tuple to another list.
  I had a list of tuples called <code>lst</code> and tried to extract the elements to a list called <code>lst2</code> and what I got was:</p>
  <pre><code>&gt;&gt;&gt; lst = [(1, 2), (3, 4), (5, 6)]
  &gt;&gt;&gt; lst2 = []
  &gt;&gt;&gt; [lst2[i] = lst[i][0] for i in range(len(lst))]
    File &quot;&lt;stdin&gt;&quot;, line 1
      [lst2[i] = lst[i][0] for i in range(len(list))]
                ^
  SyntaxError: invalid syntax
  </code></pre>
  <p>The desired output is <code>[1, 3, 5]</code>.</p>
  <p>Can you help figure out what's wrong with this syntax?</p>