[Python3 填坑] 015 __str__ 与 __repr__ 的区别

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1. print( 坑的信息 )

• 挖坑时间：2019/04/07
• 明细

坑的编码	内容
Py023-3	__str__ 与 __repr__ 的区别

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2. 开始填坑

2.1 上例子

>>> class A(object):
...     def __str__(self):
...         return "this is __str__"
...     def __repr__(self):
...         return "this is __repr__"
...
>>> a = A()
>>> a
this is __repr__
>>> print(a)
this is __str__
>>> 

2.2 关系与区别

• 同时定义 __repr__ 方法和 __str__ 方法时，print() 方法会调用 __str__ 方法

Python 3.7.3 的官方文档

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__().

• 最后一句大概是说，__str__ 是调用 __repr__ 实现的
  
  

 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.

• 最后一句大概是说，__repr__ 通常用于调试
  
  

网上看到一个例子，运行了一下

>>> import datetime
>>> today = datetime.datetime.now()
>>> today
datetime.datetime(2019, 4, 11, 20, 45, 8, 463653)
>>> str(today)
'2019-04-11 20:45:08.463653'
>>> repr(today)
'datetime.datetime(2019, 4, 11, 20, 45, 8, 463653)'
>>> 

简单地说

• __str__ 表达更简洁，__repr__ 显示更全面