>>> from marks import best_worst_mark

>>> l = [['44444444D',8.3],['11111111A',7.25],['88888888H',4.1],['22222222B',3.8],['66666666F',5.3]] 
>>> m, p = best_worst_mark(l)
>>> m
8.3
>>> p
3.8
>>> l = [['3A', 5]]
>>> m, p = best_worst_mark(l)
>>> m
5
>>> p
5
>>> l = [['1A', 2], ['2B', 1], ['3C', 4]]
>>> m, p = best_worst_mark(l)
>>> m
4
>>> p
1