[Tutor] listing all combinations of elements of a list

[Bill Kranec]

Is there a module containing a function for listing the unique k-element 
subsets of an n-item list?  I have written some code (right now I only 
need it for 2 element subsets):

def combination(items)
   list = []
   for i in range(0,len(items)):
      for j in range(0,len(items)):
         if j > i:
            list.append((list[i],list[j]))
   return list
My problems with this code being that a) code I write is usually pretty 
inefficient, b) it doesn't extend to subsets of size > 2, and c) it uses 
nested loops, which I have gathered from some previous discussions on 
this list to be less than ideal.

Any thoughts on how to improve / replace this code would be appreciated.
Thanks,
Bill
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