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创新互联Python教程:enum—-对枚举的支持

enum —- 对枚举的支持

3.4 新版功能.

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源代码: Lib/enum.py

Important

This page contains the API reference information. For tutorial information and discussion of more advanced topics, see


An enumeration:

Enumerations are created either by using class syntax, or by using function-call syntax:

 
 
 
 
  1. >>> from enum import Enum
  2. >>> # class syntax
  3. >>> class Color(Enum):
  4. ... RED = 1
  5. ... GREEN = 2
  6. ... BLUE = 3
  7. >>> # functional syntax
  8. >>> Color = Enum('Color', ['RED', 'GREEN', 'BLUE'])

Even though we can use class syntax to create Enums, Enums are not normal python classes. See How are Enums different? for more details.

备注

命名法


模块内容

EnumType

The type for Enum and its subclasses.

Enum

Base class for creating enumerated constants.

IntEnum

Base class for creating enumerated constants that are also subclasses of int. (Notes)

StrEnum

Base class for creating enumerated constants that are also subclasses of str. (Notes)

Flag

创建可与位运算符搭配使用,又不会失去 Flag 成员资格的枚举常量的基类。

IntFlag

Base class for creating enumerated constants that can be combined using the bitwise operators without losing their IntFlag membership. IntFlag members are also subclasses of int. (Notes)

ReprEnum

Used by IntEnum, StrEnum, and IntFlag to keep the str() of the mixed-in type.

EnumCheck

An enumeration with the values CONTINUOUS, NAMED_FLAGS, and UNIQUE, for use with verify() to ensure various constraints are met by a given enumeration.

FlagBoundary

An enumeration with the values STRICT, CONFORM, EJECT, and KEEP which allows for more fine-grained control over how invalid values are dealt with in an enumeration.

auto

Instances are replaced with an appropriate value for Enum members. StrEnum defaults to the lower-cased version of the member name, while other Enums default to 1 and increase from there.

property()

Allows Enum members to have attributes without conflicting with member names.

unique()

确保一个名称只绑定一个值的 Enum 类装饰器。

verify()

Enum class decorator that checks user-selectable constraints on an enumeration.

member()

Make obj a member. Can be used as a decorator.

nonmember()

Do not make obj a member. Can be used as a decorator.

global_enum()

Modify the str() and repr() of an enum to show its members as belonging to the module instead of its class. Should only be used if the enum members will be exported to the module global namespace.

show_flag_values()

Return a list of all power-of-two integers contained in a flag.

3.6 新版功能: Flag, IntFlag, auto

3.11 新版功能: StrEnum, EnumCheck, ReprEnum, FlagBoundary, property, member, nonmember, global_enum, show_flag_values


Data Types

class enum.EnumType

EnumType is the metaclass for enum enumerations. It is possible to subclass EnumType — see Subclassing EnumType for details.

EnumType is responsible for setting the correct __repr__(), __str__(), __format__(), and __reduce__() methods on the final enum, as well as creating the enum members, properly handling duplicates, providing iteration over the enum class, etc.

class enum.Enum

Enum is the base class for all enum enumerations.

备注

Using auto with Enum results in integers of increasing value, starting with 1.

class enum.IntEnum

IntEnum is the same as Enum, but its members are also integers and can be used anywhere that an integer can be used. If any integer operation is performed with an IntEnum member, the resulting value loses its enumeration status.

 
 
 
 
  1. >>> from enum import IntEnum
  2. >>> class Numbers(IntEnum):
  3. ... ONE = 1
  4. ... TWO = 2
  5. ... THREE = 3
  6. >>> Numbers.THREE
  7. >>> Numbers.ONE + Numbers.TWO
  8. 3
  9. >>> Numbers.THREE + 5
  10. 8
  11. >>> Numbers.THREE == 3
  12. True

备注

Using auto with IntEnum results in integers of increasing value, starting with 1.

在 3.11 版更改: __str__() is now int.__str__() to better support the replacement of existing constants use-case. __format__() was already int.__format__() for that same reason.

class enum.StrEnum

StrEnum is the same as Enum, but its members are also strings and can be used in most of the same places that a string can be used. The result of any string operation performed on or with a StrEnum member is not part of the enumeration.

备注

There are places in the stdlib that check for an exact str instead of a str subclass (i.e. type(unknown) == str instead of isinstance(unknown, str)), and in those locations you will need to use str(StrEnum.member).

备注

Using auto with StrEnum results in the lower-cased member name as the value.

备注

__str__() is str.__str__() to better support the replacement of existing constants use-case. __format__() is likewise str.__format__() for that same reason.

3.11 新版功能.

class enum.Flag

Flag members support the bitwise operators & (AND), | (OR), ^ (XOR), and ~ (INVERT); the results of those operators are members of the enumeration.

备注

Using auto with Flag results in integers that are powers of two, starting with 1.

在 3.11 版更改: The repr() of zero-valued flags has changed. It is now::

 
 
 
 
  1. >>> Color(0)

class enum.IntFlag

IntFlag is the same as Flag, but its members are also integers and can be used anywhere that an integer can be used.

 
 
 
 
  1. >>> from enum import IntFlag, auto
  2. >>> class Color(IntFlag):
  3. ... RED = auto()
  4. ... GREEN = auto()
  5. ... BLUE = auto()
  6. >>> Color.RED & 2
  7. >>> Color.RED | 2

If any integer operation is performed with an IntFlag member, the result is not an IntFlag:

 
 
 
 
  1. >>> Color.RED + 2
  2. 3

If a Flag operation is performed with an IntFlag member and:

  • the result is a valid IntFlag: an IntFlag is returned

  • the result is not a valid IntFlag: the result depends on the FlagBoundary setting

The repr() of unnamed zero-valued flags has changed. It is now:

 
 
 
 
  1. >>> Color(0)

备注

Using auto with IntFlag results in integers that are powers of two, starting with 1.

在 3.11 版更改: __str__() is now int.__str__() to better support the replacement of existing constants use-case. __format__() was already int.__format__() for that same reason.

class enum.ReprEnum

ReprEum uses the repr() of Enum, but the str() of the mixed-in data type:

  • int.__str__() for IntEnum and IntFlag

  • str.__str__() for StrEnum

Inherit from ReprEnum to keep the str() / :func:`format of the mixed-in data type instead of using the Enum-default str().

3.11 新版功能.

class enum.EnumCheck

EnumCheck contains the options used by the verify() decorator to ensure various constraints; failed constraints result in a ValueError.

备注

CONTINUOUS and NAMED_FLAGS are designed to work with integer-valued members.

3.11 新版功能.

class enum.FlagBoundary

FlagBoundary controls how out-of-range values are handled in Flag and its subclasses.

3.11 新版功能.


支持的 __dunder__ 名称

__members__ 是一个 member_name:member 条目的只读有序映射。 它只在类上可用。

如果指定了 __new__(),它必须创建并返回枚举成员;相应地设定成员的 _value_ 也是一个很好的主意。 一旦所有成员都创建完成它就不会再被使用。

支持的 _sunder_ 名称

3.6 新版功能: _missing_, _order_, _generate_next_value_

3.7 新版功能: _ignore_


Utilities and Decorators

class enum.auto

auto can be used in place of a value. If used, the Enum machinery will call an Enum‘s _generate_next_value_() to get an appropriate value. For Enum and IntEnum that appropriate value will be the last value plus one; for Flag and IntFlag it will be the first power-of-two greater than the last value; for StrEnum it will be the lower-cased version of the member’s name. Care must be taken if mixing auto() with manually specified values.

auto instances are only resolved when at the top level of an assignment:

  • FIRST = auto() will work (auto() is replaced with 1);
  • SECOND = auto(), -2 will work (auto is replaced with 2, so 2, -2 is

    used to create the SECOND enum member;

  • THREE = [auto(), -3] will not work (, -3 is used to create the THREE enum member)

_generate_next_value_ can be overridden to customize the values used by auto.

备注

in 3.13 the default "generate_next_value_ will always return the highest member value incremented by 1, and will fail if any member is an incompatible type.

@enum.property

A decorator similar to the built-in property, but specifically for enumerations. It allows member attributes to have the same names as members themselves.

备注

the property and the member must be defined in separate classes; for example, the value and name attributes are defined in the Enum class, and Enum subclasses can define members with the names value and name.

3.11 新版功能.

@enum.unique

A class decorator specifically for enumerations. It searches an enumeration’s __members__, gathering any aliases it finds; if any are found ValueError is raised with the details:

 
 
 
 
  1. >>> from enum import Enum, unique
  2. >>> @unique
  3. ... class Mistake(Enum):
  4. ... ONE = 1
  5. ... TWO = 2
  6. ... THREE = 3
  7. ... FOUR = 3
  8. ...
  9. Traceback (most recent call last):
  10. ...
  11. ValueError: duplicate values found in : FOUR -> THREE

@enum.verify

A class decorator specifically for enumerations. Members from EnumCheck are used to specify which constraints should be checked on the decorated enumeration.

3.11 新版功能.

@enum.member

A decorator for use in enums: its target will become a member.

3.11 新版功能.

@enum.nonmember

A decorator for use in enums: its target will not become a member.

3.11 新版功能.

@enum.global_enum

A decorator to change the str() and repr() of an enum to show its members as belonging to the module instead of its class. Should only be used when the enum members are exported to the module global namespace (see re.RegexFlag for an example).

3.11 新版功能.

enum.show_flag_values(value)

Return a list of all power-of-two integers contained in a flag value.

3.11 新版功能.


Notes

IntEnum, StrEnum, and IntFlag

These three enum types are designed to be drop-in replacements for existing integer- and string-based values; as such, they have extra limitations:

  • __str__ uses the value and not the name of the enum member

  • __format__, because it uses __str__, will also use the value of the enum member instead of its name

If you do not need/want those limitations, you can either create your own base class by mixing in the int or str type yourself:

   
   
   
   
  1. >>> from enum import Enum
  2. >>> class MyIntEnum(int, Enum):
  3. ... pass

or you can reassign the appropriate str(), etc., in your enum:

  
  
  
  
  1. >>> from enum import IntEnum
  2. >>> class MyIntEnum(IntEnum):
  3. ... __str__ = IntEnum.__str__

标题名称:创新互联Python教程:enum—-对枚举的支持
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