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
[]
'''