>>> from marathon import first_difference

>>> lt = [('Gebrmariam', 7694, 'ETH'), ('Mutai', 7758, 'KEN'),
...       ('Kipkosgei', 7839, 'KEN'), ('Goumri', 7851, 'MAR'),
...       ('Kwambai', 7891, 'KEN'), ('Keflezighi', 7898, 'USA'),
...       ('DosSantos', 7911, 'BRA')]

>>> first_difference(lt, 'dif1.txt')
>>> f1 = open ('dif1.txt', 'r')
>>> s1 = f1.read()
>>> s1
'Gebrmariam 0\nMutai 64\nKipkosgei 145\nGoumri 157\nKwambai 197\nKeflezighi 204\nDosSantos 217\n'

>>> lt = [('Kwambai', 7871, 'KEN'), ('Gebrmariam', 7894, 'ETH'),
...       ('Keflezighi', 7899, 'USA'), ('Mutai', 7931, 'KEN'),
...       ('Kipkosgei', 7956, 'KEN'), ('Goumri', 7979, 'MAR')]
>>> first_difference(lt, 'dif2.txt')
>>> f2 = open ('dif2.txt', 'r')
>>> s2 = f2.read()
>>> s2
'Kwambai 0\nGebrmariam 23\nKeflezighi 28\nMutai 60\nKipkosgei 85\nGoumri 108\n'