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 ?
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
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()
其他回答
我喜欢在Python中这样定义枚举:
class Animal:
class Dog: pass
class Cat: pass
x = Animal.Dog
这比使用整数更有漏洞,因为你不必担心确保整数是唯一的(例如,如果你说Dog = 1和Cat = 1,你就完蛋了)。
它比使用字符串更防bug,因为你不必担心拼写错误(例如。 x == "猫"无声失败,但x ==动物。Catt是一个运行时异常)。
附录: 你甚至可以通过让Dog和Cat继承一个具有正确元类的符号类来增强这个解决方案:
class SymbolClass(type):
def __repr__(self): return self.__qualname__
def __str__(self): return self.__name__
class Symbol(metaclass=SymbolClass): pass
class Animal:
class Dog(Symbol): pass
class Cat(Symbol): pass
然后,如果你使用这些值来索引一个字典,请求它的表示将使它们看起来很漂亮:
>>> mydict = {Animal.Dog: 'Wan Wan', Animal.Cat: 'Nyaa'}
>>> mydict
{Animal.Dog: 'Wan Wan', Animal.Cat: 'Nyaa'}
下面是亚历克·托马斯解决方案的一个变种:
def enum(*args, **kwargs):
return type('Enum', (), dict((y, x) for x, y in enumerate(args), **kwargs))
x = enum('POOH', 'TIGGER', 'EEYORE', 'ROO', 'PIGLET', 'RABBIT', 'OWL')
assert x.POOH == 0
assert x.TIGGER == 1
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))
我喜欢使用列表或集合作为枚举。例如:
>>> packet_types = ['INIT', 'FINI', 'RECV', 'SEND']
>>> packet_types.index('INIT')
0
>>> packet_types.index('FINI')
1
>>>
在PEP 435之前,Python没有等效的,但你可以实现自己的。
就我个人而言,我喜欢保持简单(我在网上看到过一些非常复杂的例子),就像这样……
class Animal:
DOG = 1
CAT = 2
x = Animal.DOG
在Python 3.4 (PEP 435)中,可以将Enum作为基类。这为您提供了一些额外的功能,详见PEP。例如,enum成员不同于整数,它们由名称和值组成。
from enum import Enum
class Animal(Enum):
DOG = 1
CAT = 2
print(Animal.DOG)
# <Animal.DOG: 1>
print(Animal.DOG.value)
# 1
print(Animal.DOG.name)
# "DOG"
如果您不想键入值,请使用以下快捷方式:
class Animal(Enum):
DOG, CAT = range(2)
枚举实现可以转换为列表,并且是可迭代的。其成员的顺序是声明顺序,与它们的值无关。例如:
class Animal(Enum):
DOG = 1
CAT = 2
COW = 0
list(Animal)
# [<Animal.DOG: 1>, <Animal.CAT: 2>, <Animal.COW: 0>]
[animal.value for animal in Animal]
# [1, 2, 0]
Animal.CAT in Animal
# True