>>> from marks import sort_marks

>>> l = [['44444444D',8.3],['88888888H',10.0],['22222222B',4.8],['66666666F',5.3]]
>>> sort_marks(l)
[['22222222B', 4.8], ['66666666F', 5.3], ['44444444D', 8.3], ['88888888H', 10.0]]