Python-сообщество

>>> sorted(buf,cmp = lambda x,y: cmp(x[1],y[1]))
[('a', 1), ('b', 3), ('a', 12), ('z', 20)]
>>> sorted(buf,key=lambda x: x[1])
[('a', 1), ('b', 3), ('a', 12), ('z', 20)]
>>> from operator import itemgetter
>>> sorted(buf,key=itemgetter(1))
[('a', 1), ('b', 3), ('a', 12), ('z', 20)]
>>>

>>> class Person(object):
...     def __init__(self, name, age, city):
...         self.name = name
...         self.age = age
...         self.city = city
...     def __lt__(self, other):  # сортирем по возрасту и имени
...         return (self.age, self.name) < (other.age, other.name)
...     def __repr__(self):
...         return "({0},{1},{2})".format(self.name, self.age, self.city)
...
>>> buf = [Person("Alice",21,"Redmond"),Person("Bob",20,"Boston"),
...        Person("Nadine",21,"Denver")]
>>> sorted(buf)
[(Bob,20,Boston), (Alice,21,Redmond), (Nadine,21,Denver)]

>>> def keyfunc(person):
...     return person.age, person.city
...
>>> sorted(buf, key=keyfunc)
[(Bob,20,Boston), (Nadine,21,Denver), (Alice,21,Redmond)]
>>> sorted(buf, key=lambda person: (person.age, person.city)) 
[(Bob,20,Boston), (Nadine,21,Denver), (Alice,21,Redmond)]
>>> sorted(buf, key=lambda person: (person.name, person.city))
[(Alice,21,Redmond), (Bob,20,Boston), (Nadine,21,Denver)]
>>> sorted(buf, key=lambda person: (person.name[-1], person.city)) #последняя буква имени, город
[(Bob,20,Boston), (Nadine,21,Denver), (Alice,21,Redmond)]

sorted(buf, key=lambda person: [person.name, person.city])

sorted(buf, key=lambda person: {person.name, person.city})

>>> from operator import attrgetter, itemgetter
>>> sorted(buf, key=attrgetter('age', 'city'))
[(Bob,20,Boston), (Nadine,21,Denver), (Alice,21,Redmond)]
>>> sorted([(3,1),(2,1),(4,0)], key=itemgetter(1,0))
[(4, 0), (2, 1), (3, 1)]
>>> sorted(buf, key=attrgetter('age', 'name'))
[(Bob,20,Boston), (Alice,21,Redmond), (Nadine,21,Denver)]