title: Python releasing memory of dictionary
body: <p>I'm having a problem with releasing the memory of a dictionary in Python.
  I run the following check and followed the process memory usage:</p>
  
  <pre><code>a = dict() 
  for i in xrange(1000000):
      a[i] = i
  for i in xrange(1000000):
      del a[i]
  gc.collect()
  </code></pre>
  
  <p>the memory usage after running those lines is much higher than before.
  how can I release all of the memory?
  notice I don't want to delete the dict itself.</p>
  
  <p>thanks.</p>