title: Python's itertools product memory consumption
body: <p>The <a href="http://docs.python.org/library/itertools.html#itertools.product">documentation</a> says that the cartesian product function </p>
  
  <pre><code>the actual implementation does not build up intermediate results in memory.
  </code></pre>
  
  <p>How can that be possible with generators? Can somebody show me an example
  with a bounded memory consumption for 2 generators?</p>