for i, item in enumerate(numbers):
    for j in range(i+1, len(numbers)):
        total_of_two_items = numbers[i] + numbers[j]
        if(total_of_two_items == total_number):
            print '{first_item} {second_item}'.format(first_item=i+1, second_item=j+1)
            print 'n'

n = 181
n2 = n//2
numbers = [80, 98, 83, 92, 1, 38, 37, 54, 58, 89]
goodnums = {n-x for x in numbers if x<=n2} & {x for x in numbers if x>n2}
pairs = {(n-x, x) for x in goodnums}

if not n%2 and (n2, n2) in pairs and numbers.count(n2) == 1:
   pairs.remove((n2, n2))

def mergeSort(A):

    if len(A) > 1:
        mid = len(A)//2
        lefthalf = A[:mid]
        righthalf = A[mid:]

        mergeSort(lefthalf)
        mergeSort(righthalf)

        # Merge the halves
        i,j,k=0,0,0

        while i<len(lefthalf) and j<len(righthalf):
            if lefthalf[i] < righthalf[j]:
                A[k] = lefthalf[i]
                i = i + 1
            else:
                A[k] = righthalf[j]
                j = j + 1
            k = k + 1

        while i < len(lefthalf):
            A[k] = lefthalf[i]
            k = k +1
            i = i + 1

        while j < len(righthalf):
            A[k] = righthalf[j]
            k = k + 1
            j = j + 1


def find_pairs(alist, item):
    # We take two flags left and right to point to the ends of the sorted list
    left = 0
    right = len(alist) - 1
    pairs = []
    while(left<right):
        # We find the sum of the numbers in at these two points.
        # If the sum is equal to our number for which we are finding pairs, we consider this pair and add it to our results
        # If the sum is greater than expected then we move the right pointer one step back to a smaller number and then compute sum again
        # If the sum is smaller than expected then we move the left pointer a step ahead and check the sum with a greater number
        sum = alist[left] + alist[right]
        if sum == item:
            pairs += [(alist[left],alist[right])]
            # Move the pointers to next elements in the list and find more pairs
            right -= 1
            left += 1
        elif sum > item:
            right -= 1
        else:
            left += 1
    return pairs


l1 = [80, 98, 83, 92, 1, 38, 37, 54, 58, 89]
mergeSort(l1)
print l1
print find_pairs(l1,181)

l2 = [-5,-2, -23, 34,21,90,1,0,65,8,-10]
mergeSort(l2)
print l2
print find_pairs(l2,-2)

[1, 37, 38, 54, 58, 80, 83, 89, 92, 98]
[(83, 98), (89, 92)]


[-23, -10, -5, -2, 0, 1, 8, 21, 34, 65, 90]
[(-23, 21), (-10, 8), (-2, 0)]

def sum_of_pairs_matches(K, arr):
    uniques = {i: True for i in arr}
    pairs = set()
    for val in arr:
        k = -val + K if val<K else -K - val
        if(uniques.get(k, False)):
            pairs.add(tuple(sorted([k,val])))
    return pairs

sum_of_pairs_matches(5, [-5, -4, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

{(-5, 10), (-4, 9), (-1, 6), (0, 5), (1, 4), (2, 3)}