python __call__ 方法 函数

 __call__

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)。

1. 1. class Animal(object):
   2. def __init__(self, name, legs):
   3. self.name = name
   4. self.legs = legs
   5. self.stomach = []
   6.  
   7. def __call__(self,food):
   8. self.stomach.append(food)
   9.  
   10. def poop(self):
   11. if len(self.stomach) > 0:
   12. return self.stomach.pop(0)
   13.  
   14. def __str__(self):
   15. return 'A animal named %s' % (self.name)
   16.  
   17. cow = Animal('king', 4) #We make a cow
   18. dog = Animal('flopp', 4) #We can make many animals
   19. print 'We have 2 animales a cow name %s and dog named %s,both have %s legs' % (cow.name, dog.name, cow.legs)
   20. print cow #here __str__ metod work
   21.  
   22. #We give food to cow
   23. cow('gras')
   24. print cow.stomach
   25.  
   26. #We give food to dog
   27. dog('bone')
   28. dog('beef')
   29. print dog.stomach
   30.  
   31. #What comes inn most come out
   32. print cow.poop()
   33. print cow.stomach #Empty stomach
   34.  
   35. '''-->output
   36. We have 2 animales a cow name king and dog named flopp,both have 4 legs
   37. A animal named king
   38. ['gras']
   39. ['bone', 'beef']
   40. gras
   41. []
   42. '''