[已解决]__str__ 和__repr__的区别？

shuofxz

小甲鱼在视频里举了两个例子

1. >>> class A():
   
2.         def __str__(self):
   
3.                 return "Aloha!"
   
4. 
   
5.        
   
6. >>> a = A()
   
7. >>> a
   
8. <__main__.A object at 0x0000000003BA8588>
   
9. >>> print(a)
   
10. Aloha!

复制代码

1. >>> class A():
   
2.         def __repr__(self):
   
3.                 return "Hello!"
   
4. 
   
5. >>> a = A()
   
6. >>> a
   
7. Hello!

复制代码

但我还是不太明白是怎么用的，这两个又有什么区别，在什么时候调用这两个函数？

最佳答案

月排行榜 / 总排行榜

hldh214

2016-2-2 11:36:50

shuofxz 发表于 2016-2-2 10:54
这个啥也没写呀

都告诉你了是定义对象调用什么方法了, 查手册呀

object.__str__(self)
Called by str(object) and the built-in functions format() and print() to compute the “informal” or nicely printable string representation of an object. The return value must be a string object.

This method differs from object.__repr__() in that there is no expectation that __str__() return a valid Python expression: a more convenient or concise representation can be used.

The default implementation defined by the built-in type object calls object.__repr__().

object.__repr__(self)
Called by the repr() built-in function to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <...some useful description...> should be returned. The return value must be a string object. If a class defines __repr__() but not __str__(), then __repr__() is also used when an “informal” string representation of instances of that class is required.

This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.

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hldh214

http://bbs.fishc.com/forum.php?mod=viewthread&tid=48793

shuofxz

hldh214 发表于 2016-2-2 10:45
http://bbs.fishc.com/forum.php?mod=viewthread&tid=48793

这个啥也没写呀

hldh214

shuofxz 发表于 2016-2-2 10:54
这个啥也没写呀

都告诉你了是定义对象调用什么方法了, 查手册呀

object.__str__(self)
Called by str(object) and the built-in functions format() and print() to compute the “informal” or nicely printable string representation of an object. The return value must be a string object.

This method differs from object.__repr__() in that there is no expectation that __str__() return a valid Python expression: a more convenient or concise representation can be used.

The default implementation defined by the built-in type object calls object.__repr__().

object.__repr__(self)
Called by the repr() built-in function to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <...some useful description...> should be returned. The return value must be a string object. If a class defines __repr__() but not __str__(), then __repr__() is also used when an “informal” string representation of instances of that class is required.

This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.

shuofxz

这里面还是没有说明问题呀
为什么第一个例子要print(a) 才能显示return的字符串
第二个例子只用 a 就能显示return的字符串