我主要是c#开发人员，但我目前正在用Python开发一个项目。
我如何在Python中表示等价的Enum ?
当前回答
有趣的是，前几天我正好需要这个，但我找不到一个值得使用的实现……所以我自己写了:
import functools
class EnumValue(object):
def __init__(self,name,value,type):
self.__value=value
self.__name=name
self.Type=type
def __str__(self):
return self.__name
def __repr__(self):#2.6 only... so change to what ever you need...
return '{cls}({0!r},{1!r},{2})'.format(self.__name,self.__value,self.Type.__name__,cls=type(self).__name__)
def __hash__(self):
return hash(self.__value)
def __nonzero__(self):
return bool(self.__value)
def __cmp__(self,other):
if isinstance(other,EnumValue):
return cmp(self.__value,other.__value)
else:
return cmp(self.__value,other)#hopefully their the same type... but who cares?
def __or__(self,other):
if other is None:
return self
elif type(self) is not type(other):
raise TypeError()
return EnumValue('{0.Name} | {1.Name}'.format(self,other),self.Value|other.Value,self.Type)
def __and__(self,other):
if other is None:
return self
elif type(self) is not type(other):
raise TypeError()
return EnumValue('{0.Name} & {1.Name}'.format(self,other),self.Value&other.Value,self.Type)
def __contains__(self,other):
if self.Value==other.Value:
return True
return bool(self&other)
def __invert__(self):
enumerables=self.Type.__enumerables__
return functools.reduce(EnumValue.__or__,(enum for enum in enumerables.itervalues() if enum not in self))
@property
def Name(self):
return self.__name
@property
def Value(self):
return self.__value
class EnumMeta(type):
@staticmethod
def __addToReverseLookup(rev,value,newKeys,nextIter,force=True):
if value in rev:
forced,items=rev.get(value,(force,()) )
if forced and force: #value was forced, so just append
rev[value]=(True,items+newKeys)
elif not forced:#move it to a new spot
next=nextIter.next()
EnumMeta.__addToReverseLookup(rev,next,items,nextIter,False)
rev[value]=(force,newKeys)
else: #not forcing this value
next = nextIter.next()
EnumMeta.__addToReverseLookup(rev,next,newKeys,nextIter,False)
rev[value]=(force,newKeys)
else:#set it and forget it
rev[value]=(force,newKeys)
return value
def __init__(cls,name,bases,atts):
classVars=vars(cls)
enums = classVars.get('__enumerables__',None)
nextIter = getattr(cls,'__nextitr__',itertools.count)()
reverseLookup={}
values={}
if enums is not None:
#build reverse lookup
for item in enums:
if isinstance(item,(tuple,list)):
items=list(item)
value=items.pop()
EnumMeta.__addToReverseLookup(reverseLookup,value,tuple(map(str,items)),nextIter)
else:
value=nextIter.next()
value=EnumMeta.__addToReverseLookup(reverseLookup,value,(str(item),),nextIter,False)#add it to the reverse lookup, but don't force it to that value
#build values and clean up reverse lookup
for value,fkeys in reverseLookup.iteritems():
f,keys=fkeys
for key in keys:
enum=EnumValue(key,value,cls)
setattr(cls,key,enum)
values[key]=enum
reverseLookup[value]=tuple(val for val in values.itervalues() if val.Value == value)
setattr(cls,'__reverseLookup__',reverseLookup)
setattr(cls,'__enumerables__',values)
setattr(cls,'_Max',max([key for key in reverseLookup] or [0]))
return super(EnumMeta,cls).__init__(name,bases,atts)
def __iter__(cls):
for enum in cls.__enumerables__.itervalues():
yield enum
def GetEnumByName(cls,name):
return cls.__enumerables__.get(name,None)
def GetEnumByValue(cls,value):
return cls.__reverseLookup__.get(value,(None,))[0]
class Enum(object):
__metaclass__=EnumMeta
__enumerables__=None
class FlagEnum(Enum):
@staticmethod
def __nextitr__():
yield 0
for val in itertools.count():
yield 2**val
def enum(name,*args):
return EnumMeta(name,(Enum,),dict(__enumerables__=args))
接受或离开它，它做了我需要它做的:)
像这样使用它:
class Air(FlagEnum):
__enumerables__=('None','Oxygen','Nitrogen','Hydrogen')
class Mammals(Enum):
__enumerables__=('Bat','Whale',('Dog','Puppy',1),'Cat')
Bool = enum('Bool','Yes',('No',0))
其他回答
我使用元类来实现枚举(在我的想法中，它是一个const)。代码如下:
class ConstMeta(type):
'''
Metaclass for some class that store constants
'''
def __init__(cls, name, bases, dct):
'''
init class instance
'''
def static_attrs():
'''
@rtype: (static_attrs, static_val_set)
@return: Static attributes in dict format and static value set
'''
import types
attrs = {}
val_set = set()
#Maybe more
filter_names = set(['__doc__', '__init__', '__metaclass__', '__module__', '__main__'])
for key, value in dct.iteritems():
if type(value) != types.FunctionType and key not in filter_names:
if len(value) != 2:
raise NotImplementedError('not support for values that is not 2 elements!')
#Check value[0] duplication.
if value[0] not in val_set:
val_set.add(value[0])
else:
raise KeyError("%s 's key: %s is duplicated!" % (dict([(key, value)]), value[0]))
attrs[key] = value
return attrs, val_set
attrs, val_set = static_attrs()
#Set STATIC_ATTRS to class instance so that can reuse
setattr(cls, 'STATIC_ATTRS', attrs)
setattr(cls, 'static_val_set', val_set)
super(ConstMeta, cls).__init__(name, bases, dct)
def __getattribute__(cls, name):
'''
Rewrite the special function so as to get correct attribute value
'''
static_attrs = object.__getattribute__(cls, 'STATIC_ATTRS')
if name in static_attrs:
return static_attrs[name][0]
return object.__getattribute__(cls, name)
def static_values(cls):
'''
Put values in static attribute into a list, use the function to validate value.
@return: Set of values
'''
return cls.static_val_set
def __getitem__(cls, key):
'''
Rewrite to make syntax SomeConstClass[key] works, and return desc string of related static value.
@return: Desc string of related static value
'''
for k, v in cls.STATIC_ATTRS.iteritems():
if v[0] == key:
return v[1]
raise KeyError('Key: %s does not exists in %s !' % (str(key), repr(cls)))
class Const(object):
'''
Base class for constant class.
@usage:
Definition: (must inherit from Const class!
>>> class SomeConst(Const):
>>> STATUS_NAME_1 = (1, 'desc for the status1')
>>> STATUS_NAME_2 = (2, 'desc for the status2')
Invoke(base upper SomeConst class):
1) SomeConst.STATUS_NAME_1 returns 1
2) SomeConst[1] returns 'desc for the status1'
3) SomeConst.STATIC_ATTRS returns {'STATUS_NAME_1': (1, 'desc for the status1'), 'STATUS_NAME_2': (2, 'desc for the status2')}
4) SomeConst.static_values() returns set([1, 2])
Attention:
SomeCosnt's value 1, 2 can not be duplicated!
If WrongConst is like this, it will raise KeyError:
class WrongConst(Const):
STATUS_NAME_1 = (1, 'desc for the status1')
STATUS_NAME_2 = (1, 'desc for the status2')
'''
__metaclass__ = ConstMeta
##################################################################
#Const Base Class ends
##################################################################
def main():
class STATUS(Const):
ERROR = (-3, '??')
OK = (0, '??')
print STATUS.ERROR
print STATUS.static_values()
print STATUS.STATIC_ATTRS
#Usage sample:
user_input = 1
#Validate input:
print user_input in STATUS.static_values()
#Template render like:
print '<select>'
for key, value in STATUS.STATIC_ATTRS.items():
print '<option value="%s">%s</option>' % (value[0], value[1])
print '</select>'
if __name__ == '__main__':
main()
有趣的是，前几天我正好需要这个，但我找不到一个值得使用的实现……所以我自己写了:
import functools
class EnumValue(object):
def __init__(self,name,value,type):
self.__value=value
self.__name=name
self.Type=type
def __str__(self):
return self.__name
def __repr__(self):#2.6 only... so change to what ever you need...
return '{cls}({0!r},{1!r},{2})'.format(self.__name,self.__value,self.Type.__name__,cls=type(self).__name__)
def __hash__(self):
return hash(self.__value)
def __nonzero__(self):
return bool(self.__value)
def __cmp__(self,other):
if isinstance(other,EnumValue):
return cmp(self.__value,other.__value)
else:
return cmp(self.__value,other)#hopefully their the same type... but who cares?
def __or__(self,other):
if other is None:
return self
elif type(self) is not type(other):
raise TypeError()
return EnumValue('{0.Name} | {1.Name}'.format(self,other),self.Value|other.Value,self.Type)
def __and__(self,other):
if other is None:
return self
elif type(self) is not type(other):
raise TypeError()
return EnumValue('{0.Name} & {1.Name}'.format(self,other),self.Value&other.Value,self.Type)
def __contains__(self,other):
if self.Value==other.Value:
return True
return bool(self&other)
def __invert__(self):
enumerables=self.Type.__enumerables__
return functools.reduce(EnumValue.__or__,(enum for enum in enumerables.itervalues() if enum not in self))
@property
def Name(self):
return self.__name
@property
def Value(self):
return self.__value
class EnumMeta(type):
@staticmethod
def __addToReverseLookup(rev,value,newKeys,nextIter,force=True):
if value in rev:
forced,items=rev.get(value,(force,()) )
if forced and force: #value was forced, so just append
rev[value]=(True,items+newKeys)
elif not forced:#move it to a new spot
next=nextIter.next()
EnumMeta.__addToReverseLookup(rev,next,items,nextIter,False)
rev[value]=(force,newKeys)
else: #not forcing this value
next = nextIter.next()
EnumMeta.__addToReverseLookup(rev,next,newKeys,nextIter,False)
rev[value]=(force,newKeys)
else:#set it and forget it
rev[value]=(force,newKeys)
return value
def __init__(cls,name,bases,atts):
classVars=vars(cls)
enums = classVars.get('__enumerables__',None)
nextIter = getattr(cls,'__nextitr__',itertools.count)()
reverseLookup={}
values={}
if enums is not None:
#build reverse lookup
for item in enums:
if isinstance(item,(tuple,list)):
items=list(item)
value=items.pop()
EnumMeta.__addToReverseLookup(reverseLookup,value,tuple(map(str,items)),nextIter)
else:
value=nextIter.next()
value=EnumMeta.__addToReverseLookup(reverseLookup,value,(str(item),),nextIter,False)#add it to the reverse lookup, but don't force it to that value
#build values and clean up reverse lookup
for value,fkeys in reverseLookup.iteritems():
f,keys=fkeys
for key in keys:
enum=EnumValue(key,value,cls)
setattr(cls,key,enum)
values[key]=enum
reverseLookup[value]=tuple(val for val in values.itervalues() if val.Value == value)
setattr(cls,'__reverseLookup__',reverseLookup)
setattr(cls,'__enumerables__',values)
setattr(cls,'_Max',max([key for key in reverseLookup] or [0]))
return super(EnumMeta,cls).__init__(name,bases,atts)
def __iter__(cls):
for enum in cls.__enumerables__.itervalues():
yield enum
def GetEnumByName(cls,name):
return cls.__enumerables__.get(name,None)
def GetEnumByValue(cls,value):
return cls.__reverseLookup__.get(value,(None,))[0]
class Enum(object):
__metaclass__=EnumMeta
__enumerables__=None
class FlagEnum(Enum):
@staticmethod
def __nextitr__():
yield 0
for val in itertools.count():
yield 2**val
def enum(name,*args):
return EnumMeta(name,(Enum,),dict(__enumerables__=args))
接受或离开它，它做了我需要它做的:)
像这样使用它:
class Air(FlagEnum):
__enumerables__=('None','Oxygen','Nitrogen','Hydrogen')
class Mammals(Enum):
__enumerables__=('Bat','Whale',('Dog','Puppy',1),'Cat')
Bool = enum('Bool','Yes',('No',0))
使用下面的方法。
TYPE = {'EAN13': u'EAN-13',
'CODE39': u'Code 39',
'CODE128': u'Code 128',
'i25': u'Interleaved 2 of 5',}
>>> TYPE.items()
[('EAN13', u'EAN-13'), ('i25', u'Interleaved 2 of 5'), ('CODE39', u'Code 39'), ('CODE128', u'Code 128')]
>>> TYPE.keys()
['EAN13', 'i25', 'CODE39', 'CODE128']
>>> TYPE.values()
[u'EAN-13', u'Interleaved 2 of 5', u'Code 39', u'Code 128']
我用它来选择Django模型，它看起来非常python化。它不是一个真正的Enum，但它完成了这项工作。
这是我见过的最好的一个:“Python中的First Class Enums”
http://code.activestate.com/recipes/413486/
It gives you a class, and the class contains all the enums. The enums can be compared to each other, but don't have any particular value; you can't use them as an integer value. (I resisted this at first because I am used to C enums, which are integer values. But if you can't use it as an integer, you can't use it as an integer by mistake so overall I think it is a win.) Each enum is a unique value. You can print enums, you can iterate over them, you can test that an enum value is "in" the enum. It's pretty complete and slick.
编辑(cfi):上面的链接不兼容Python 3。下面是我将枚举.py移植到Python 3的端口:
def cmp(a,b):
if a < b: return -1
if b < a: return 1
return 0
def Enum(*names):
##assert names, "Empty enums are not supported" # <- Don't like empty enums? Uncomment!
class EnumClass(object):
__slots__ = names
def __iter__(self): return iter(constants)
def __len__(self): return len(constants)
def __getitem__(self, i): return constants[i]
def __repr__(self): return 'Enum' + str(names)
def __str__(self): return 'enum ' + str(constants)
class EnumValue(object):
__slots__ = ('__value')
def __init__(self, value): self.__value = value
Value = property(lambda self: self.__value)
EnumType = property(lambda self: EnumType)
def __hash__(self): return hash(self.__value)
def __cmp__(self, other):
# C fans might want to remove the following assertion
# to make all enums comparable by ordinal value {;))
assert self.EnumType is other.EnumType, "Only values from the same enum are comparable"
return cmp(self.__value, other.__value)
def __lt__(self, other): return self.__cmp__(other) < 0
def __eq__(self, other): return self.__cmp__(other) == 0
def __invert__(self): return constants[maximum - self.__value]
def __nonzero__(self): return bool(self.__value)
def __repr__(self): return str(names[self.__value])
maximum = len(names) - 1
constants = [None] * len(names)
for i, each in enumerate(names):
val = EnumValue(i)
setattr(EnumClass, each, val)
constants[i] = val
constants = tuple(constants)
EnumType = EnumClass()
return EnumType
if __name__ == '__main__':
print( '\n*** Enum Demo ***')
print( '--- Days of week ---')
Days = Enum('Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su')
print( Days)
print( Days.Mo)
print( Days.Fr)
print( Days.Mo < Days.Fr)
print( list(Days))
for each in Days:
print( 'Day:', each)
print( '--- Yes/No ---')
Confirmation = Enum('No', 'Yes')
answer = Confirmation.No
print( 'Your answer is not', ~answer)
对于旧的Python 2.x
def enum(*sequential, **named):
enums = dict(zip(sequential, [object() for _ in range(len(sequential))]), **named)
return type('Enum', (), enums)
如果你命名它，是你的问题，但如果不创建对象而不是值允许你这样做:
>>> DOG = enum('BARK', 'WALK', 'SIT')
>>> CAT = enum('MEOW', 'WALK', 'SIT')
>>> DOG.WALK == CAT.WALK
False
当使用这里的其他实现时(在我的例子中使用命名实例时)，必须确保永远不要尝试比较来自不同枚举的对象。这里有一个可能的陷阱:
>>> DOG = enum('BARK'=1, 'WALK'=2, 'SIT'=3)
>>> CAT = enum('WALK'=1, 'SIT'=2)
>>> pet1_state = DOG.BARK
>>> pet2_state = CAT.WALK
>>> pet1_state == pet2_state
True
呵!
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