SumPairs.py

list1 = [1,2,2,3,4,5,6,9]
def pair_sums(nums,n):
    dict_nums = {}
    result = []
    nums.sort()
    for val in nums:
        if dict_nums.has_key(val):
            dict_nums[val] += 1
        else:
             dict_nums[val] = 1
    #print dict_nums       
    for val in dict_nums:
        diff = n-val
        #print diff
        neededVal = diff
        if dict_nums.has_key(neededVal) and (neededVal!= val or dict_nums[neededVal]>1) and val<=neededVal:
            result.append([val,neededVal])
        
    return result    

print pair_sums(list1,4)
'''and (dict_nums[neededVal]!= neededVal or dict_nums[neededVal]>1)'''