python中List的sort方法指南

> students = [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10),] 

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

> sorted(students, cmp=lambda x,y : cmp(x[2], y[2])) # sort by age 
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)] 

> from operator import itemgetter, attrgetter 
> sorted(students, key=itemgetter(2)) 

> sorted(students, key=itemgetter(1,2)) # sort by grade then by age 
[('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)] 

> d = {'data1':3, 'data2':1, 'data3':2, 'data4':4} 
> sorted(d.iteritems(), key=itemgetter(1), reverse=True) 
[('data4', 4), ('data1', 3), ('data3', 2), ('data2', 1)] 

class itemgetter(__builtin__.object) 
| itemgetter(item, ...) --> itemgetter object 
| 
| Return a callable object that fetches the given item(s) from its operand. 
| After, f=itemgetter(2), the call f(r) returns r[2]. 
| After, g=itemgetter(2,5,3), the call g(r) returns (r[2], r[5], r[3]) 

def itemgetter(i,*a):  
  def func(obj):  
    r = obj[i]  
    if a:  
      r = (r,) + tuple(obj[i] for i in a)  
    return r  
  return func  
 
> a = [1,2,3]  
> b=operator.itemgetter(1)  
> b(a)  
2  
> b=operator.itemgetter(1,0)  
> b(a)  
(2, 1)  
> b=itemgetter(1)  
> b(a)  
2  
> b=itemgetter(1,0)  
> b(a)  
(2, 1)