可以视lambda为一个简易的函数，它不需要return,形式简单
#冒号左边是变量
#冒号右边是返回值
例：
>>> def f (x): return x**2
...
>>> print f(8)
64 >>>
>>> g = lambda x: x**2
>>>
>>> print g(8)
64
>>> foo = [2, 18, 9, 22, 17, 24, 8, 12, 27]
>>>
>>> print filter(lambda x: x % 3 == 0, foo)
[18, 9, 24, 12, 27] >>>
>>> print map(lambda x: x * 2 + 10, foo)
[14, 46, 28, 54, 44, 58, 26, 34, 64] >>>
>>> print reduce(lambda x, y: x + y, foo)
139