英文:
How does python3.11's StrEnum's MRO work differently for __str__ and __repr__?
问题
Python 3.11引入了StrEnum和IntEnum，它们分别继承自str或int，并且还继承自ReprEnum，而ReprEnum则继承自Enum。
ReprEnum的实现实际上是空的。
>>> print(inspect.getsource(ReprEnum))class ReprEnum(Enum):"""Only changes the repr(), leaving str() and format() to the mixed-in type."""
如果我创建一个StrEnum并检查其MRO，我可以看到str排在第一位。
class Strings(StrEnum):A = "a"
>>> Strings.__mro__(<enum 'Strings'>, <enum 'StrEnum'>, <class 'str'>, <enum 'ReprEnum'>, <enum 'Enum'>, <class 'object'>)
str和Enum都定义了__str__和__repr__方法。
>>> str.__repr__<slot wrapper '__repr__' of 'str' objects>>>> str.__str__<slot wrapper '__str__' of 'str' objects>>>> Enum.__repr__<function Enum.__repr__ at 0x7ffff69f72e0>>>> Enum.__str__<function Enum.__str__ at 0x7ffff69f7380>
那么，__repr__如何从Enum继承，而__str__如何从str继承呢？
英文:
Python3.11 introduced StrEnum and IntEnum which inherit str or int respectively, and also inherit ReprEnum, which in turn inherits Enum.
ReprEnum's implementation is actually empty.
>>> print(inspect.getsource(ReprEnum))class ReprEnum(Enum):"""Only changes the repr(), leaving str() and format() to the mixed-in type."""
If I create a StrEnum and check the MRO, I can see that str comes first.
class Strings(StrEnum):A = "a"
>>> Strings.__mro__(<enum 'Strings'>, <enum 'StrEnum'>, <class 'str'>, <enum 'ReprEnum'>, <enum 'Enum'>, <class 'object'>)
Both str and Enum define a __str__ and a __repr__
>>> str.__repr__<slot wrapper '__repr__' of 'str' objects>>>> str.__str__<slot wrapper '__str__' of 'str' objects>>>> Enum.__repr__<function Enum.__repr__ at 0x7ffff69f72e0>>>> Enum.__str__<function Enum.__str__ at 0x7ffff69f7380>
How then does __repr__ get inherited from Enum and __str__ get inherited from str?
答案1
得分: 3
`__repr__` 方法以正常方式继承自 `Enum`（通过 `StrEnum`）```python>>> Strings.__repr__ is StrEnum.__repr__ is Enum.__repr__True
对于 __str__ 方法，元类 EnumType 检查了 ReprEnum 的存在，并在类定义时将混入数据类型的 str 和 format 处理“提升”到类命名空间中 这里：
class EnumType(type):...def __new__(metacls, cls, bases, classdict, *, boundary=None, _simple=False, **kwds):...# 同样，对于 ReprEnum 的特殊处理if ReprEnum is not None and ReprEnum in bases:if member_type is object:raise TypeError('ReprEnum 子类必须与数据类型（即 int、str、float 等）混合使用')if '__format__' not in classdict:enum_class.__format__ = member_type.__format__classdict['__format__'] = enum_class.__format__if '__str__' not in classdict:method = member_type.__str__if method is object.__str__:# 如果 member_type 没有定义 __str__，object.__str__ 将使用其 __repr__，# 所以我们也将使用其 __repr__method = member_type.__repr__enum_class.__str__ = methodclassdict['__str__'] = enum_class.__str__...
现在 Strings.__str__ 方法可以直接在类命名空间中找到，不需要遍历 MRO。
<details><summary>英文:</summary>The `__repr__` method comes the normal way, inherited from `Enum` (via `StrEnum`)
>>> Strings.repr is StrEnum.repr is Enum.repr
True
For the `__str__` method, the metaclass `EnumType` checks for the presence of `ReprEnum` and "hoists up" the `str` and `format` handling of the mixed-in data type into the class namespace at class definition time [here](https://github.com/python/cpython/blob/v3.11.4/Lib/enum.py#L575-L592):
class EnumType(type):
...def __new__(metacls, cls, bases, classdict, *, boundary=None, _simple=False, **kwds):...# Also, special handling for ReprEnumif ReprEnum is not None and ReprEnum in bases:if member_type is object:raise TypeError('ReprEnum subclasses must be mixed with a data type (i.e.'' int, str, float, etc.)')if '__format__' not in classdict:enum_class.__format__ = member_type.__format__classdict['__format__'] = enum_class.__format__if '__str__' not in classdict:method = member_type.__str__if method is object.__str__:# if member_type does not define __str__, object.__str__ will use# its __repr__ instead, so we'll also use its __repr__method = member_type.__repr__enum_class.__str__ = methodclassdict['__str__'] = enum_class.__str__...
Now that a `Strings.__str__` method may be found directly in the class namespace, the MRO needn't be traversed.</details>
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