Given a list: l1: ['a', 'b', 'c', 'a', 'a', 'b'] output: ['a', 'b', 'c', 'a'_1, 'a'_2, 'b'_1 ] I created the following code to get the output. Its messyyy.. for index in range(len(l1)): counter = 1 list_of_duplicates_for_item = [dup_index for dup_index, item in enumerate(l1) if item == l1[index] and l1.count(l1[index]) > 1] for dup_index in list_of_duplicates_for_item[1:]: l1[dup_index] = l1[dup_index] + '_' + str(counter) counter = counter + 1 Is there a more pythonic way of doing this? I couldnt find anything on the web.