Enum的使用记录。
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参考链接：Python_枚举
我自己的使用感受，枚举就像定义了一套变量赋值关系，这套赋值关系就一个对象，你可以通过对象里面的key或者value来找到对象本身。
使用起来还时蛮有意思的。
使用中，你可以通过创建类，继承使用。或者直接通过Enum(‘xx‘,‘xxx xxx xxx‘)来使用。
首先通过创建类来使用：
In [71]: class My_Enum(Enum):
...: name = ‘sidian‘
...: age = 18
...: adde = ‘hangzhou‘
...:
In [72]: My_Enum.name # 通过类属性来知道关系对象
Out[72]: <My_Enum.name: ‘sidian‘>
In [73]: dir(My_Enum.name) # 产看对象的一些属性，竟然没有看到那么的属性
Out[73]: [‘__class__‘, ‘__doc__‘, ‘__module__‘, ‘value‘]
In [74]: My_Enum.name.value # 查看对象的值
Out[74]: ‘sidian‘
In [75]: My_Enum(‘sidian‘) # 通过实例化值来找到关系对象实例
Out[75]: <My_Enum.name: ‘sidian‘>
In [76]: x = My_Enum(‘sidian‘)
In [77]: x
Out[77]: <My_Enum.name: ‘sidian‘>
In [78]: dir(x)
Out[78]: [‘__class__‘, ‘__doc__‘, ‘__module__‘, ‘value‘]
In [79]: x.name # 虽然没有name属性，但从name属性还时拿到了关系对象的name
Out[79]: ‘name‘
In [80]: dir(My_Enum)
Out[80]: [‘__class__‘, ‘__doc__‘, ‘__members__‘, ‘__module__‘, ‘adde‘, ‘age‘, ‘name‘]
In [81]: My_Enum.__members__ # 通过__members__属性可以看到内部的成员为不可变的字典，key为类属性的字符串形式，value为关系对象。
Out[81]:
mappingproxy({‘name‘: <My_Enum.name: ‘sidian‘>,
‘age‘: <My_Enum.age: 18>,
‘adde‘: <My_Enum.adde: ‘hangzhou‘>})
In [82]:
还有一种就是直接实例化Enum类
In [88]: my_son = Enum(‘son‘,‘dabao erbao sanbao‘)
In [89]: my_son # 通过实例化创建对象
Out[89]: <enum ‘son‘>
In [90]: My_Enum # 对前面通过继承的类名调用，发现该类名已经是Enum的实例，Enum给我的感觉像类元。
Out[90]: <enum ‘My_Enum‘>
In [91]: my_son.__members__ # Enum里面的参数，第一个是实例后的对象名称，后面的参数空格会自动切割，然后自动给分割后的变量名复制，复制初始值从1开始
Out[91]:
mappingproxy({‘dabao‘: <son.dabao: 1>,
‘erbao‘: <son.erbao: 2>,
‘sanbao‘: <son.sanbao: 3>})
In [92]: my_son(2) # 通过值寻找关系对象
Out[92]: <son.erbao: 2>
In [93]: my_son(2).name
Out[93]: ‘erbao‘
In [94]: my_love = Enum(‘love‘,[‘l1‘,‘l2‘]) # 实例化的第二个参数也可以通过列表进行传入
In [95]: my_love
Out[95]: <enum ‘love‘>
In [96]: my_love(1)
Out[96]: <love.l1: 1>
In [97]: my_love(2)
Out[97]: <love.l2: 2>
In [98]:
In [100]: Enum? Init signature: Enum(value, names=None, *, module=None, qualname=None, type=None, start=1) Docstring: Generic enumeration. Derive from this class to define new enumerations. File: /usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/enum.py Type: EnumMeta Subclasses: IntEnum, Flag, Purpose, _SendfileMode, SortKey, s, Color, 12, Status, Gender, ... In [101]:
下面上原码
Init signature: Enum(value, names=None, *, module=None, qualname=None, type=None, start=1)
Source:
class Enum(metaclass=EnumMeta):
"""Generic enumeration.
Derive from this class to define new enumerations.
"""
def __new__(cls, value):
# all enum instances are actually created during class construction
# without calling this method; this method is called by the metaclass‘
# __call__ (i.e. Color(3) ), and by pickle
if type(value) is cls:
# For lookups like Color(Color.RED)
return value
# by-value search for a matching enum member
# see if it‘s in the reverse mapping (for hashable values)
try:
return cls._value2member_map_[value]
except KeyError:
# Not found, no need to do long O(n) search
pass
except TypeError:
# not there, now do long search -- O(n) behavior
for member in cls._member_map_.values():
if member._value_ == value:
return member
# still not found -- try _missing_ hook
try:
exc = None
result = cls._missing_(value)
except Exception as e:
exc = e
result = None
if isinstance(result, cls):
return result
else:
ve_exc = ValueError("%r is not a valid %s" % (value, cls.__name__))
if result is None and exc is None:
raise ve_exc
elif exc is None:
exc = TypeError(
‘error in %s._missing_: returned %r instead of None or a valid member‘
% (cls.__name__, result)
)
exc.__context__ = ve_exc
raise exc
def _generate_next_value_(name, start, count, last_values):
for last_value in reversed(last_values):
try:
return last_value + 1
except TypeError:
pass
else:
return start
@classmethod
def _missing_(cls, value):
raise ValueError("%r is not a valid %s" % (value, cls.__name__))
def __repr__(self):
return "<%s.%s: %r>" % (
self.__class__.__name__, self._name_, self._value_)
def __str__(self):
return "%s.%s" % (self.__class__.__name__, self._name_)
def __dir__(self):
added_behavior = [
m
for cls in self.__class__.mro()
for m in cls.__dict__
if m[0] != ‘_‘ and m not in self._member_map_
]
return ([‘__class__‘, ‘__doc__‘, ‘__module__‘] + added_behavior)
def __format__(self, format_spec):
# mixed-in Enums should use the mixed-in type‘s __format__, otherwise
# we can get strange results with the Enum name showing up instead of
# the value
# pure Enum branch
if self._member_type_ is object:
cls = str
val = str(self)
# mix-in branch
else:
cls = self._member_type_
val = self._value_
return cls.__format__(val, format_spec)
def __hash__(self):
return hash(self._name_)
def __reduce_ex__(self, proto):
return self.__class__, (self._value_, )
# DynamicClassAttribute is used to provide access to the `name` and
# `value` properties of enum members while keeping some measure of
# protection from modification, while still allowing for an enumeration
# to have members named `name` and `value`. This works because enumeration
# members are not set directly on the enum class -- __getattr__ is
# used to look them up.
@DynamicClassAttribute
def name(self):
"""The name of the Enum member."""
return self._name_
@DynamicClassAttribute
def value(self):
"""The value of the Enum member."""
return self._value_
@classmethod
def _convert(cls, name, module, filter, source=None):
"""
Create a new Enum subclass that replaces a collection of global constants
"""
# convert all constants from source (or module) that pass filter() to
# a new Enum called name, and export the enum and its members back to
# module;
# also, replace the __reduce_ex__ method so unpickling works in
# previous Python versions
module_globals = vars(sys.modules[module])
if source:
source = vars(source)
else:
source = module_globals
# We use an OrderedDict of sorted source keys so that the
# _value2member_map is populated in the same order every time
# for a consistent reverse mapping of number to name when there
# are multiple names for the same number rather than varying
# between runs due to hash randomization of the module dictionary.
members = [
(name, source[name])
for name in source.keys()
if filter(name)]
try:
# sort by value
members.sort(key=lambda t: (t[1], t[0]))
except TypeError:
# unless some values aren‘t comparable, in which case sort by name
members.sort(key=lambda t: t[0])
cls = cls(name, members, module=module)
cls.__reduce_ex__ = _reduce_ex_by_name
module_globals.update(cls.__members__)
module_globals[name] = cls
return cls
File: /usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/enum.py
Type: EnumMeta
Subclasses: IntEnum, Flag, Purpose, _SendfileMode, SortKey, s, Color, 12, Status, Gender, ...
(END)
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