自定义输出内容 __str__() 和 __repr__() 以及__format__() 的使用

 1 class DemoClass:
 2     def __init__(self,name,age):
 3         self.name = name
 4         self.age = age
 5 
 6     def __str__(self):
 7         #print()-->调它
 8         return "Name:{},Age:{}".format(self.name,self.age)
 9 
10 
11 if __name__ == "__main__":
12     demo = DemoClass("tom",18)
13     print(demo)  #此时调用的是demo.__str__()  
14     #如果不重写__str__() 输出的就是 <__main__.DemoClass object at 0x00000238B1D6FBE0>
15 ‘‘‘
16     输出：
17     Name:tom,Age:18
18 ‘‘‘

 1 class DemoClass:
 2     def __init__(self,name,age):
 3         self.name = name
 4         self.age = age
 5 
 6     def __repr__(self):
 7         #print()-->调它
 8         return "Name:{},Age:{}".format(self.name,self.age)
 9 
10     def __str__(self):
11         return "name:{},age:{}".format(self.name,self.age)
12 
13 if __name__ == "__main__":
14     demo = DemoClass("tom",18)
15     print(demo)
16     
17 ‘‘‘
18     输出：
19     name:tom,age:18
20     
21     结果表明，print() 的调用顺序是：
22     print()-->str()-->demo.__str__()-->demo.__repr__()
　　　　不过，__repr__() 适合在交互环境下使用！
23 ‘‘‘

 1 format_dict = {
 2     ‘ymd‘: "{0.year} {0.mon} {0.day}",
 3     ‘y:m:d‘: "{0.year}:{0.mon}:{0.day}",
 4     ‘y-m-d‘: "{0.year}-{0.mon}-{0.day}",
 5     #0 代表的是类的实例对象self
 6 }
 7 class DemoClass:
 8     def __init__(self, year, mon, day):
 9         self.year = year
10         self.mon = mon
11         self.day = day
12 
13     def __format__(self, key):
14         return format_dict[key].format(self)
15 
16 
17 if __name__ == "__main__":
18     demo = DemoClass(2019, 8, 6)
19     print(format(demo, ‘ymd‘))
20     print(format(demo, ‘y:m:d‘))
21     print(format(demo, ‘y-m-d‘))
22 ‘‘‘
23     输出      
24     2019 8 6
25     2019:8:6
26     2019-8-6
27 ‘‘‘