>>> class A(object):
... def __repr__(self):
... return "this is __repr__"
... def __str__(self):
... return "this is __str__"
...
>>> a = A()
>>> a
this is __repr__
>>> print(a)
this is __str__
>>>
官方文档
Python 3.7.3
__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.
__repr__() 通常用于调试
它能将对象转化为供解释器读取的形式（字符串）
__str__()
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__().