我想在我的 python Flags 枚举中有一个“ALL”标志
myenum.EVERY_MEMBER & myenum.ALL == myenum.EVERY_MEMBER
成立。我目前有:
from enum import Flag, auto
class RefreshFlags(Flag):
NONE = 0
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
.....
因为这个枚举可能会在任何开发状态下增长,所以我希望有类似的东西
@property
def ALL(self):
retval = self.NONE
for member in self.__members__.values():
retval |= member
return retval
这不起作用:
RefreshFlags.EVENTS & RefreshFlags.ALL
TypeError: unsupported operand type(s) for &: 'RefreshFlags' and 'property'
请注意,此问题目前仅与 python 3.6 或更高版本相关。
有几种方法可以解决这个问题:
使用
classproperty
(参见Zero's answer
)MSeifert's answer
)currently buggy
)创建一个新的基类(见下文)
使用类属性方法需要注意的一件事是,由于描述符是在类上定义的,而不是在元类上定义的,因此不存在针对设置和删除的通常保护措施 - 换句话说:
>>> RefreshFlags.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
>>> RefreshFlags.ALL = 'oops'
>>> RefreshFlags.ALL
'oops'
创建一个新的基类:
# lightly tested
from enum import Flag, auto
from operator import or_ as _or_
from functools import reduce
class AllFlag(Flag):
@classproperty
def ALL(cls):
cls_name = cls.__name__
if not len(cls):
raise AttributeError('empty %s does not have an ALL value' % cls_name)
value = cls(reduce(_or_, cls))
cls._member_map_['ALL'] = value
return value
使用中:
class RefreshFlag(AllFlag):
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
>>> RefreshFlag.ALL
<RefreshFlag.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
ALL
属性中有趣的区别是 _member_map_
中的名称设置——这允许为 Enum 成员提供相同的保护:
>>> RefreshFlag.ALL = 9
Traceback (most recent call last):
....
AttributeError: Cannot reassign members.
但是,这里有一个竞争条件:如果
RefreshFlag.ALL = ...
发生在之前RefreshFlag.ALL
第一次被激活,那么它就会被破坏;出于这个原因,我将在这种情况下使用装饰器,因为装饰器将在枚举被破坏之前对其进行处理。
# lightly tested
from enum import Flag, auto
from operator import or_ as _or_
from functools import reduce
def with_limits(enumeration):
"add NONE and ALL psuedo-members to enumeration"
none_mbr = enumeration(0)
all_mbr = enumeration(reduce(_or_, enumeration))
enumeration._member_map_['NONE'] = none_mbr
enumeration._member_map_['ALL'] = all_mbr
return enumeration
使用中:
@with_limits
class RefreshFlag(Flag):
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
>>> RefreshFlag.ALL = 99
Traceback (most recent call last):
...
AttributeError: Cannot reassign members.
>>> RefreshFlag.ALL
<RefreshFlag.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
>>> RefreshFlag.NONE
<RefreshFlag.0: 0>
TL;DR 因为属性仅在类的实例上评估,而
__members__
只能在类上访问。
如果您在课程上访问
property
,它只会返回 property
:
>>> RefreshFlags.ALL
<property at 0x2a5d93382c8>
要使其工作,您需要将其设为类方法:
from enum import Flag, auto
class RefreshFlags(Flag):
NONE = 0
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
@classmethod
def ALL(cls):
retval = self.NONE
for member in cls.__members__.values():
retval |= member
return retval
>>> RefreshFlags.ALL()
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
或访问实例上的属性:
from enum import Flag, auto
class RefreshFlags(Flag):
NONE = 0
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
@property
def ALL(self):
retval = self.NONE
# One needs to access .__class__ here!
for member in self.__class__.__members__.values():
retval |= member
return retval
>>> RefreshFlags.EVENTS.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
在这两种情况下,您都可以稍后进行比较:
>>> RefreshFlags.EVENTS & RefreshFlags.EVENTS.ALL
<RefreshFlags.EVENTS: 1>
您在评论中表示您希望
ALL
成员表现得像其他成员一样,在这种情况下,我建议使用类装饰器:
def with_ALL_member(enumeration):
retval = enumeration(0) # in case NONE is not defined
for name, member in enumeration.__members__.items():
retval |= member
enumeration.ALL = retval
return enumeration
@with_ALL_member
class RefreshFlags(Flag):
NONE = 0
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
>>> RefreshFlags.EVENTS & RefreshFlags.ALL
<RefreshFlags.EVENTS: 1>
>>> RefreshFlags.DEFENSES & RefreshFlags.ALL
<RefreshFlags.DEFENSES: 8>
类装饰器也可以用于其他枚举:)
按照 MSeifert 的 answer,可以编写一个
@classproperty
装饰器,它允许您直接将 RefreshFlags.ALL
作为属性(而不是作为常规方法或实例上的属性)访问:
from enum import Flag, auto
from operator import or_
from functools import reduce
class classproperty:
def __init__(self, func):
self._func = func
def __get__(self, obj, owner):
return self._func(owner)
class RefreshFlags(Flag):
NONE = 0
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
@classproperty
def ALL(cls):
return reduce(or_, cls)
您当然可以使用显式的
ALL()
循环编写 for
,如您的示例所示;以上仅作为替代方案提供。
>>> RefreshFlags.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
>>> RefreshFlags.ALL & RefreshFlags.BUILDINGS
<RefreshFlags.BUILDINGS: 4>
这是一个稍微更紧凑的解决方案,使用更精简的描述符,这使得它更容易重用。
class _all:
def __get__(self, instance, cls):
return ~cls(0)
class RefreshFlags(Flag):
EVENTS = auto()
RESOURCES = auto()
BUILDINGS = auto()
DEFENSES = auto()
ALL = _all()
RefreshFlags.ALL
>>> <RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
正如已经指出的,以这种方式定义的成员不会包含在命名空间的
_member_map_
字典中,
因此它不受覆盖保护。
获取所有
Flag
的一个简单方法是 ~RefreshFlags(0)
,它给出 RefreshFlags.EVENTS|RESOURCES|BUILDINGS|DEFENSES|
(注意按声明顺序排序)。