lambda 表达式

lambda 表达式用来声明 匿名函数：没有名字的小函数。
lambda 表达式只能包含一个表达式，不允许其他复杂语句，但在表达式中可以调用其他函数，支持默认值参数和关键参数。
lambda 表达式的计算结果相当于函数的返回值。

>>>f=lambda x,y,z:x+y+z
>>>print(f(1,2,3))
6
>>>g=lambda x,y=2,z=3:x+y+z
>>>print(g(1))
6
>>>print(g(2,z=4,y=5))
11
>>>L=[(lambda x:x**2),(lambda x:x**3),(lambda x:x**3)]
>>>print(L[0](2), L[1](2), L[2](2))
4 8 16
>>>D={‘f1’:(lambda:2+3), ‘f2’:(lambda:2*3), ‘f3’:(lambda:2**3)}
>>>print(D[‘f1’](), D[‘f2’](), D[‘f3’]())
5 6 8
>>>L=[1,2,3,4,5]
>>>print(map( (lambda x:x+10), L))
[11,12,13,14,15]
>>>L
[1,2,3,4,5]
>>>def demo(n):
return n*n
>>>demo(5)
25
>>>a_list=[1,2,3,4,5]
>>>map(lambda x: demo(x),a_list)
[1,4,9,16,25]
>>>data=list(range(20))
>>>print(data)
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]

>>>import random
>>>random.shuffle(data)
>>>data
[4,3,11,13,12,15,9,2,10,6,19,18,14,8,0,7,5,17,1,16]

>>>data.sort(key=lambda x:x)
>>>data
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]

>>>data.sort(key=lambda x:len(str(x)))
>>>data
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]

>>>data.sort(key=lambda x:len(str(x)), reverse=True)
>>>data
[10,11,12,13,14,15,16,17,18,19,0,1,2,3,4,5,6,7,8,9]