The __str__ method in Python represents the class objects as a string – it can be used for classes. The __str__ method should be defined in a way that is easy to read and outputs all the members of the class. This method is also used as a debugging tool when the members of a class need to be checked.
The __str__ method is called when the following functions are invoked on the object and return a string:
If we have not defined the __str__, then it will call the __repr__ method. The __repr__ method returns a string that describes the pointer of the object by default (if the programmer does not define it).
原文：https://www.cnblogs.com/shamoguzhou/p/15239988.html