python特殊方法定制类

#coding:utf-8
class RoundFloat(object):
    def __init__(self,val):
        assert isinstance(val, float),"value must be a float"
        self.value = round(val,2)
    def __str__(self):
        return "{:.2f}".format(self.value)

    __repr__ = __str__
    #def __repr__(self):
       # return self.__str__()

r = RoundFloat(3.1567)
print r
print type(r)

output result:

3.16
<class '__main__.RoundFloat'>