Python中有一個有趣的語法，只要定義類型的時候，實現__call__函數，這個類型就成為可調用的。
換句話說，我們可以把這個類型的對象當作函數來使用，相當于 重載了括號運算符。

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

計算地球場景的時候，我們就可以令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 cowdog = Animal('flopp', 4) #We can make many animalsprint '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 cowcow('gras')print cow.stomach #We give food to dogdog('bone')dog('beef')print dog.stomach #What comes inn most come outprint cow.poop()print cow.stomach #Empty stomach '''-->outputWe have 2 animales a cow name king and dog named flopp,both have 4 legsA animal named king['gras']['bone', 'beef']gras[]'''