title: When are parentheses required around a tuple?
body: <p>Is there a reference somewhere defining precisely when enclosing tuples with parentheses is or is not required?  </p>
  
  <p>Here is an example that surprised me recently:</p>
  
  <pre><code>&gt;&gt;&gt; d = {}
  &gt;&gt;&gt; d[0,] = 'potato'
  &gt;&gt;&gt; if 0, in d:
    File "&lt;stdin&gt;", line 1
      if 0, in d:
          ^
  SyntaxError: invalid syntax
  </code></pre>