在python中排序枚举值

Question

我希望能够安排 Enum 的排序。有人建议如何解决这个问题？

以下枚举元类正在使用：

class EnumMeta(type):
    def __new__(typ, name, bases, attrs):
        cls_attrs = {}
        cls_choices = []
        for attr_name, value in attrs.items():
            cls_attrs[attr_name] = attr_name.lower()
            if not attr_name.startswith("__"):
                cls_choices.append((attr_name.lower(), value))

        def choices(cls):
            return cls_choices

        def values(cls, value=None):
            if value is None:
                return {choice[0]: unicode(choice[1]) for choice in cls.choices()}
            elif isinstance(value, list):
                return {choice[0]: unicode(choice[1]) for choice in cls.choices() if choice[0] in value}
            else:
                return unicode(dict(cls.choices()).get(value))

        def keys(cls, nil=False):
            items = [item[0] for item in cls.choices()]
            if nil:
                items.append('')

            return items

        def combined_length(cls):
            return len(",".join(cls.values().keys()))

        def max_length(cls):
            return max(map(len, cls.values().keys()))

        cls_attrs['choices'] = classmethod(choices)
        cls_attrs['values'] = classmethod(values)
        cls_attrs['keys'] = classmethod(keys)
        cls_attrs['combined_length'] = classmethod(combined_length)
        cls_attrs['max_length'] = classmethod(max_length)

        return type(name, bases, cls_attrs)

一个枚举的例子如下：

class SideHemType:
    __ordering__ = ['double', 'single']
    __metaclass__ = EnumMeta

    Single = "Single side hem for opaque fabrics"
    Double = "Double side hem for transparent fabrics"


  class TestEnumOrdering:
        print SideHemType.keys()
        print SideHemType.values() 

通过打印 Enum SideHemType，首先打印 Double，然后打印 Single。但我想先单，然后双。

Answer 1

如果您使用的是 Python3.4，则可以使用新的 enum.Enum 类型，它会记住声明枚举成员的顺序。

如果您使用的是较早的 Python，则应使用可用的 enum34 包 from PyPI，它支持 Python 回到 2.4。

enum34 包，如果在 Python3 中使用，也会记住成员声明的顺序。如果在 Python 2 中使用，它支持额外的 _order_ 属性：

from enum import Enum

class SideHemType(Enum):

    _order_ = 'Single Double'  # only needed in Python 2

    Single = "Single side hem for opaque fabrics"
    Double = "Double side hem for transparent fabrics"

    @classmethod
    def combined_length(cls):
        return len(",".join(mbr.name for mbr in cls))

    @classmethod
    def max_length(cls):
        return max(map(len, (mbr.name for mbr in cls)))


print list(SideHemType)  # [SideHemType.Single, SideHemType.Double]

print SideHemType.Double.value  # "Double side hem for transparent fabrics"

Answer 2

使用enum 包中的IntEnum 并使用整数值指定您想要的顺序：

class Shape(IntEnum):
    CIRCLE = 1
    SQUARE = 2
Shape.CIRCLE < Shape.SQUARE

打印True。

Answer 3

您的 Enum 在 3 个地方失去了排序。首先，类主体上的属性存储在字典中，然后将项目复制到另一个字典中。最后你的 values() 返回第三个字典。字典不保存排序，无法获取类体内属性的排序。

有了这个系统，最简单的就是有一个变量

__ordering__ = [ 'single', 'double' ]

并使values() 返回一个元组列表（如dict.items()）。

class EnumMeta(type):
    def __new__(typ, name, bases, attrs):
        cls_attrs = {}
        cls_choices = {}

        for attr_name, value in attrs.items():
            cls_attrs[attr_name] = attr_name.lower()
            if not attr_name.startswith("__"):
                cls_choices[attr_name.lower()] = value

        ordering = attrs.get('__ordering__')
        if ordering == None:
            ordering = sorted(cls_choices.keys())

        def choices(cls):
            return dict(cls_choices)

        def values(cls, value=None):
            if value is None:
                return [ (k, cls_choices[k] ) for k in ordering ]
            elif not isinstance(value, basestring):
                return [ (k, cls_choices[k] ) for k in value ]
            else:
                return unicode(cls_choices.get(value))

        def keys(cls, nil=False):
            items = list(ordering)
            if nil:
                items.append('')

            return items

        def combined_length(cls):
            return len(",".join(cls.values().keys()))

        def max_length(cls):
            return max(map(len, cls.values().keys()))

        cls_attrs['choices'] = classmethod(choices)
        cls_attrs['values'] = classmethod(values)
        cls_attrs['keys'] = classmethod(keys)
        cls_attrs['combined_length'] = classmethod(combined_length)
        cls_attrs['max_length'] = classmethod(max_length)

        return type(name, bases, cls_attrs)

class SideHemType:
    __ordering__ = ['double', 'single']
    __metaclass__ = EnumMeta

    Single = "Single side hem for opaque fabrics"
    Double = "Double side hem for transparent fabrics"


print SideHemType.keys()
print SideHemType.values()