Multidimensional sort

[termiflyer]

How do I sort this:

>>> a
[['3', ['1', '0']], ['4', ['3', '0'], ['2', '0']]]

where the list can be arbitrarily large by the 3rd dimension (i
think).  E.g.:

>>> a
[['3', ['1', '0']], ['4', ['2', '0'], ['3', '0']]]


Thanks