Python中有趣在__call__函数

Python中有一个有趣的语法，只要定义类型的时候，实现call函数，这个类型就成为可调用的。
换句话说，我们可以把这个类型的对象当作函数来使用，相当于 重载了括号运算符。

    class g_dpm(object):
    def __init__(self, g):
    self.g = g
    def __call__(self, t):
    return (self.g*t**2)/2

计算地球场景的时候，我们就可以令e_dpm = g_dpm(9.8)，s = e_dpm(t)。

    class Animal(object):
      def __init__(self, name, legs):
        self.name = name
        self.legs = legs
        self.stomach = []    

      def __call__(self,food):
        self.stomach.append(food)

      def poop(self):
        if len(self.stomach) > 0:
          return self.stomach.pop(0)

      def __str__(self):    
        return 'A animal named %s' % (self.name)    

    cow = Animal('king', 4) #We make a cow
    dog = Animal('flopp', 4) #We can make many animals
    print 'We have 2 animales a cow name %s and dog named %s,both have %s legs' % (cow.name, dog.name, cow.legs)
    print cow #here __str__ metod work

    #We give food to cow
    cow('gras')
    print cow.stomach

    #We give food to dog
    dog('bone')
    dog('beef')
    print dog.stomach

    #What comes inn most come out
    print cow.poop()
    print cow.stomach #Empty stomach

    '''-->output
    We have 2 animales a cow name king and dog named flopp,both have 4 legs
    A animal named king
    ['gras']
    ['bone', 'beef']
    gras
    []
    '''