请问按老师的代码写，结果为什么是bound method.....

class Programer(object):
    hobby='play computer'
    def __init__(self,name,age,weight):
        self.name=name
        self._age=age
        self.__weight=weight
    def self_intro(self):
        print 'my name is %s \nI am %s years old\n' % (self.name, self._age)
class BackendProgramer(Programer):
    def __init__(self,name,age,weight,language):
        super(BackendProgramer,self).__init__(name,age,weight)
        self.language = language
    def self_intro(self):
        print 'my name is %s \nmy favourite language is %s\n' % (self.name, self.language)
def intro(i):
    if isinstance(i,Programer):
        print i.self_intro
if __name__=='__main__':
    prog = Programer('Albert',25,'80')
    back_prog = BackendProgramer('Alex',23,'80','Ruby')
    intro(prog)
    intro(back_prog)

运行结果是：

<bound method Programer.self_intro of <__main__.Programer object at 0x030A5490>>

<bound method BackendProgramer.self_intro of <__main__.BackendProgramer object at 0x030A5510>>