Python: сортировка массива (INTEGER, STRING)

>>> student_tuples = [
        ('john', 'A', 15),
        ('jane', 'B', 12),
        ('dave', 'B', 10),
]
>>> sorted(student_tuples, key=lambda student: student[2])   # sort by age
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

In [3]: a = [
   ...:  (1, "ABC", "BC12"),
   ...:  (2, "BCD", "BC23"),
   ...:  (3, "DEF", "BC34"),
   ...: ]

In [4]: 

In [4]: sorted(a, key=lambda x: x[1], reverse=True)
Out[4]: [(3, 'DEF', 'BC34'), (2, 'BCD', 'BC23'), (1, 'ABC', 'BC12')]

nodes = ...
def sortByFirst(item):
  return item[0]
nodes.sort(key=sortByFirst)
print nodes