ListSumAndAppend

list = [[1, 3], [1, 7], [1, 2] , [3, 4] , [3, 5] , [7, 2]]
list_out =  [{1, 3, 3}, {1, 7, 10}, {1, 2, 12}, {3, 4, 4} , {3, 5, 9} , {7, 2, 2}]

for i in range(len(list)):
    add = list[i][1]
    for j in range(i):
        if list[i][0] == list[j][0]:
            add = add+list[j][1]
    list[i].append(add)

OUT = list