title: Deleting main object by deleting reference
body: <p>I am working with large nested dictionaries, and am trying to delete nested subdictionaries.  I am wondering why the following behavior occurs. </p>
  
  <p>When I set a reference to dictionary d (called ref), then I change ref and print d, it shows an updated version of d with the third element added. </p>
  
  <pre><code>input:
  d={"a":1,"b":2}
  ref=d
  ref["c"]=3
  print(d)
  
  output:
  {'a': 1, 'b': 2, 'c': 3}
  </code></pre>
  
  <p>Given this behavior, I was expecting to be able to delete the dictionary by delete</p>
  
  <pre><code>input:
  d={"a":1,"b":2}
  ref=d
  del ref
  print(d)
  
  output:
  {'a': 1, 'b': 2}
  </code></pre>
  
  <p>I am wondering if there is a way to delete the original object when I delete the reference (meaning that the output of the second program would be an error because d was deleted.</p>