枚举 - 枚举类型

该enum模块定义了具有迭代和比较功能的枚举类型。它可用于为值创建定义明确的符号，而不是使用文字整数或字符串。

创建枚举

class通过子类化Enum和添加描述值的类属性，使用语法 定义新的枚举。

enum_create.py

import enum
class BugStatus(enum.Enum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
print('\nMember name: {}'.format(BugStatus.wont_fix.name))
print('Member value: {}'.format(BugStatus.wont_fix.value))

在Enum解析类时，将成员转换为实例。每个实例都具有name与成员名称value对应的属性以及与在类定义中分配给名称的值对应的属性。

$ python3 enum_create.py
Member name: wont_fix
Member value: 4

迭代

迭代枚举类会产生枚举的各个成员。

enum_iterate.py

import enum
class BugStatus(enum.Enum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
for status in BugStatus:
 print('{:15} = {}'.format(status.name, status.value))

成员按照在类定义中声明的顺序生成。名称和值不用于以任何方式对它们进行排序。

$ python3 enum_iterate.py
new = 7
incomplete = 6
invalid = 5
wont_fix = 4
in_progress = 3
fix_committed = 2
fix_released = 1

比较枚举

由于枚举成员未被排序，因此它们仅支持通过标识和相等性进行比较。

enum_comparison.py

import enum
class BugStatus(enum.Enum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
actual_state = BugStatus.wont_fix
desired_state = BugStatus.fix_released
print('Equality:',
 actual_state == desired_state,
 actual_state == BugStatus.wont_fix)
print('Identity:',
 actual_state is desired_state,
 actual_state is BugStatus.wont_fix)
print('Ordered by value:')
try:
 print('\n'.join(' ' + s.name for s in sorted(BugStatus)))
except TypeError as err:
 print(' Cannot sort: {}'.format(err))

大于和小于比较运算符引发 TypeError异常。

$ python3 enum_comparison.py
Equality: False True
Identity: False True
Ordered by value:
 Cannot sort: '<' not supported between instances of 'BugStatus
' and 'BugStatus'

将IntEnum类用于枚举，其中成员需要表现得更像数字 - 例如，以支持比较。

enum_intenum.py

import enum
class BugStatus(enum.IntEnum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
print('Ordered by value:')
print('\n'.join(' ' + s.name for s in sorted(BugStatus)))
$ python3 enum_intenum.py
Ordered by value:
 fix_released
 fix_committed
 in_progress
 wont_fix
 invalid
 incomplete
 new

唯一枚举值

具有相同值的枚举成员将作为对同一成员对象的别名引用进行跟踪。别名不会导致重复值存在于迭代器中Enum。

enum_aliases.py

import enum
class BugStatus(enum.Enum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
 by_design = 4
 closed = 1
for status in BugStatus:
 print('{:15} = {}'.format(status.name, status.value))
print('\nSame: by_design is wont_fix: ',
 BugStatus.by_design is BugStatus.wont_fix)
print('Same: closed is fix_released: ',
 BugStatus.closed is BugStatus.fix_released)

因为by_design并且closed是其他成员的别名，所以当迭代时，它们不会在输出中单独出现 Enum。成员的规范名称是附加到值的第一个名称。

$ python3 enum_aliases.py
new = 7
incomplete = 6
invalid = 5
wont_fix = 4
in_progress = 3
fix_committed = 2
fix_released = 1
Same: by_design is wont_fix: True
Same: closed is fix_released: True

要要求所有成员都具有唯一值，请将@unique 装饰器添加到Enum。

enum_unique_enforce.py

import enum
@enum.unique
class BugStatus(enum.Enum):
 new = 7
 incomplete = 6
 invalid = 5
 wont_fix = 4
 in_progress = 3
 fix_committed = 2
 fix_released = 1
 # This will trigger an error with unique applied.
 by_design = 4
 closed = 1

具有重复值的成员在解释类ValueError时会触发异常Enum。

$ python3 enum_unique_enforce.py
Traceback (most recent call last):
 File "enum_unique_enforce.py", line 11, in <module>
 class BugStatus(enum.Enum):
 File ".../lib/python3.6/enum.py", line 834, in unique
 (enumeration, alias_details))
ValueError: duplicate values found in <enum 'BugStatus'>:
by_design -> wont_fix, closed -> fix_released

以编程方式创建枚举

在某些情况下，以编程方式创建枚举更方便，而不是在类定义中对它们进行硬编码。对于这些情况，Enum还支持将成员名称和值传递给类构造函数。

enum_programmatic_create.py

import enum
BugStatus = enum.Enum(
 value='BugStatus',
 names=('fix_released fix_committed in_progress '
 'wont_fix invalid incomplete new'),
)
print('Member: {}'.format(BugStatus.new))
print('\nAll members:')
for status in BugStatus:
 print('{:15} = {}'.format(status.name, status.value))

该value参数是枚举，其被用于建立成员的表示的名称。该names参数列表枚举的成员。当传递单个字符串时，它将在空格和逗号上拆分，并且生成的标记将用作成员的名称，这些成员将自动分配以值开头的值1。

$ python3 enum_programmatic_create.py
Member: BugStatus.new
All members:
fix_released = 1
fix_committed = 2
in_progress = 3
wont_fix = 4
invalid = 5
incomplete = 6
new = 7

为了更好地控制与成员关联的值， names可以使用两部分元组序列或将名称映射到值的字典替换字符串。

enum_programmatic_mapping.py

import enum
BugStatus = enum.Enum(
 value='BugStatus',
 names=[
 ('new', 7),
 ('incomplete', 6),
 ('invalid', 5),
 ('wont_fix', 4),
 ('in_progress', 3),
 ('fix_committed', 2),
 ('fix_released', 1),
 ],
)
print('All members:')
for status in BugStatus:
 print('{:15} = {}'.format(status.name, status.value))

在此示例中，给出了由两部分组成的元组的列表，而不是仅包含成员名称的单个字符串。这使得可以BugStatus使用与定义的版本相同的顺序重建枚举的枚举enum_create.py。

$ python3 enum_programmatic_mapping.py
All members:
new = 7
incomplete = 6
invalid = 5
wont_fix = 4
in_progress = 3
fix_committed = 2
fix_released = 1

非整数成员值

枚举成员值不限于整数。实际上，任何类型的对象都可以与成员相关联。如果值是元组，则成员将作为单独的参数传递给__init__()。

enum_tuple_values.py

import enum
class BugStatus(enum.Enum):
 new = (7, ['incomplete',
 'invalid',
 'wont_fix',
 'in_progress'])
 incomplete = (6, ['new', 'wont_fix'])
 invalid = (5, ['new'])
 wont_fix = (4, ['new'])
 in_progress = (3, ['new', 'fix_committed'])
 fix_committed = (2, ['in_progress', 'fix_released'])
 fix_released = (1, ['new'])
 def __init__(self, num, transitions):
 self.num = num
 self.transitions = transitions
 def can_transition(self, new_state):
 return new_state.name in self.transitions
print('Name:', BugStatus.in_progress)
print('Value:', BugStatus.in_progress.value)
print('Custom attribute:', BugStatus.in_progress.transitions)
print('Using attribute:',
 BugStatus.in_progress.can_transition(BugStatus.new))

在此示例中，每个成员值是一个元组，其中包含数字ID（例如可能存储在数据库中）和远离当前状态的有效转换列表。

$ python3 enum_tuple_values.py
Name: BugStatus.in_progress
Value: (3, ['new', 'fix_committed'])
Custom attribute: ['new', 'fix_committed']
Using attribute: True

对于更复杂的情况，元组可能变得笨拙。由于成员值可以是任何类型的对象，因此字典可用于存在大量单独属性以跟踪每个枚举值的情况。复数值直接传递给 __init__()除了以外的唯一参数self。

enum_complex_values.py

import enum
class BugStatus(enum.Enum):
 new = {
 'num': 7,
 'transitions': [
 'incomplete',
 'invalid',
 'wont_fix',
 'in_progress',
 ],
 }
 incomplete = {
 'num': 6,
 'transitions': ['new', 'wont_fix'],
 }
 invalid = {
 'num': 5,
 'transitions': ['new'],
 }
 wont_fix = {
 'num': 4,
 'transitions': ['new'],
 }
 in_progress = {
 'num': 3,
 'transitions': ['new', 'fix_committed'],
 }
 fix_committed = {
 'num': 2,
 'transitions': ['in_progress', 'fix_released'],
 }
 fix_released = {
 'num': 1,
 'transitions': ['new'],
 }
 def __init__(self, vals):
 self.num = vals['num']
 self.transitions = vals['transitions']
 def can_transition(self, new_state):
 return new_state.name in self.transitions
print('Name:', BugStatus.in_progress)
print('Value:', BugStatus.in_progress.value)
print('Custom attribute:', BugStatus.in_progress.transitions)
print('Using attribute:',
 BugStatus.in_progress.can_transition(BugStatus.new))

此示例使用字典而不是元组表示与上一示例相同的数据。

$ python3 enum_complex_values.py
Name: BugStatus.in_progress
Value: {'num': 3, 'transitions': ['new', 'fix_committed']}
Custom attribute: ['new', 'fix_committed']
Using attribute: True