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
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