how to kill dictionary entry

[dsavitsk]

i have a daemon process running that keeps track of connections to it in a
dictionary.  when a client disconnects i set the dictionary value = None,
but the key persists.  is there a way to get rid of it totally? for example,
in the code below, i want a[1] and a[2] to throw the same error.

>>> a = {}
>>> a[1] = None
>>> print a[1]
None
>>> print a[2]
Traceback (innermost last):
  File "<interactive input>", line 1, in ?
KeyError: 2

thanks,
doug