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
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。
其他回答
在Java pre-JDK 5中使用的类型安全枚举模式有一个 优势的数量。就像Alexandru的回答一样,你创建了一个 类和类级别字段是枚举值;然而,枚举 值是类的实例,而不是小整数。这已经 优点是枚举值不会在不经意间比较相等 对于小整数,你可以控制它们的打印方式,任意添加 方法(如果有用的话),并使用isinstance进行断言:
class Animal:
def __init__(self, name):
self.name = name
def __str__(self):
return self.name
def __repr__(self):
return "<Animal: %s>" % self
Animal.DOG = Animal("dog")
Animal.CAT = Animal("cat")
>>> x = Animal.DOG
>>> x
<Animal: dog>
>>> x == 1
False
python-dev上最近的一个线程指出,在野外有几个枚举库,包括:
flufl.enum lazr.enum ... 和富有想象力的enum
这个解决方案是获取定义为列表的枚举类的简单方法(没有更多烦人的整数赋值):
enumeration.py:
import new
def create(class_name, names):
return new.classobj(
class_name, (object,), dict((y, x) for x, y in enumerate(names))
)
example.py:
import enumeration
Colors = enumeration.create('Colors', (
'red',
'orange',
'yellow',
'green',
'blue',
'violet',
))
我非常喜欢Alec Thomas的解决方案(http://stackoverflow.com/a/1695250):
def enum(**enums):
'''simple constant "enums"'''
return type('Enum', (object,), enums)
它看起来优雅而简洁,但它只是一个创建具有指定属性的类的函数。
通过对函数进行一些修改,我们可以让它表现得更像“枚举”:
注意:我通过尝试重现 pygtk的新样式'enums'的行为(如gtk . messagtype . warning)
def enum_base(t, **enums):
'''enums with a base class'''
T = type('Enum', (t,), {})
for key,val in enums.items():
setattr(T, key, T(val))
return T
这将基于指定类型创建枚举。除了像前面的函数那样提供属性访问外,它的行为与您期望Enum对类型的行为一样。它还继承了基类。
例如,整数enum:
>>> Numbers = enum_base(int, ONE=1, TWO=2, THREE=3)
>>> Numbers.ONE
1
>>> x = Numbers.TWO
>>> 10 + x
12
>>> type(Numbers)
<type 'type'>
>>> type(Numbers.ONE)
<class 'Enum'>
>>> isinstance(x, Numbers)
True
用这个方法还可以做一件有趣的事情,那就是通过覆盖内置方法来定制特定的行为:
def enum_repr(t, **enums):
'''enums with a base class and repr() output'''
class Enum(t):
def __repr__(self):
return '<enum {0} of type Enum({1})>'.format(self._name, t.__name__)
for key,val in enums.items():
i = Enum(val)
i._name = key
setattr(Enum, key, i)
return Enum
>>> Numbers = enum_repr(int, ONE=1, TWO=2, THREE=3)
>>> repr(Numbers.ONE)
'<enum ONE of type Enum(int)>'
>>> str(Numbers.ONE)
'1'
我喜欢Java枚举,这就是我在Python中的做法:
def enum(clsdef):
class Enum(object):
__slots__=tuple([var for var in clsdef.__dict__ if isinstance((getattr(clsdef, var)), tuple) and not var.startswith('__')])
def __new__(cls, *args, **kwargs):
if not '_the_instance' in cls.__dict__:
cls._the_instance = object.__new__(cls, *args, **kwargs)
return cls._the_instance
def __init__(self):
clsdef.values=lambda cls, e=Enum: e.values()
clsdef.valueOf=lambda cls, n, e=self: e.valueOf(n)
for ordinal, key in enumerate(self.__class__.__slots__):
args=getattr(clsdef, key)
instance=clsdef(*args)
instance._name=key
instance._ordinal=ordinal
setattr(self, key, instance)
@classmethod
def values(cls):
if not hasattr(cls, '_values'):
cls._values=[getattr(cls, name) for name in cls.__slots__]
return cls._values
def valueOf(self, name):
return getattr(self, name)
def __repr__(self):
return ''.join(['<class Enum (', clsdef.__name__, ') at ', str(hex(id(self))), '>'])
return Enum()
示例使用:
i=2
@enum
class Test(object):
A=("a",1)
B=("b",)
C=("c",2)
D=tuple()
E=("e",3)
while True:
try:
F, G, H, I, J, K, L, M, N, O=[tuple() for _ in range(i)]
break;
except ValueError:
i+=1
def __init__(self, name="default", aparam=0):
self.name=name
self.avalue=aparam
所有类变量都定义为元组,就像构造函数一样。到目前为止,还不能使用命名参数。
以下是我认为有价值的方法:
允许>和<基于枚举中的顺序进行比较,而不是词法顺序 可以地址项目的名称,属性或索引:x.a, x['a']或x[0] 支持[:]或[-1]等切片操作
最重要的是防止不同类型的枚举之间的比较!
基于http://code.activestate.com/recipes/413486-first-class-enums-in-python。
这里包含了许多文档测试,以说明这种方法的不同之处。
def enum(*names):
"""
SYNOPSIS
Well-behaved enumerated type, easier than creating custom classes
DESCRIPTION
Create a custom type that implements an enumeration. Similar in concept
to a C enum but with some additional capabilities and protections. See
http://code.activestate.com/recipes/413486-first-class-enums-in-python/.
PARAMETERS
names Ordered list of names. The order in which names are given
will be the sort order in the enum type. Duplicate names
are not allowed. Unicode names are mapped to ASCII.
RETURNS
Object of type enum, with the input names and the enumerated values.
EXAMPLES
>>> letters = enum('a','e','i','o','u','b','c','y','z')
>>> letters.a < letters.e
True
## index by property
>>> letters.a
a
## index by position
>>> letters[0]
a
## index by name, helpful for bridging string inputs to enum
>>> letters['a']
a
## sorting by order in the enum() create, not character value
>>> letters.u < letters.b
True
## normal slicing operations available
>>> letters[-1]
z
## error since there are not 100 items in enum
>>> letters[99]
Traceback (most recent call last):
...
IndexError: tuple index out of range
## error since name does not exist in enum
>>> letters['ggg']
Traceback (most recent call last):
...
ValueError: tuple.index(x): x not in tuple
## enums must be named using valid Python identifiers
>>> numbers = enum(1,2,3,4)
Traceback (most recent call last):
...
AssertionError: Enum values must be string or unicode
>>> a = enum('-a','-b')
Traceback (most recent call last):
...
TypeError: Error when calling the metaclass bases
__slots__ must be identifiers
## create another enum
>>> tags = enum('a','b','c')
>>> tags.a
a
>>> letters.a
a
## can't compare values from different enums
>>> letters.a == tags.a
Traceback (most recent call last):
...
AssertionError: Only values from the same enum are comparable
>>> letters.a < tags.a
Traceback (most recent call last):
...
AssertionError: Only values from the same enum are comparable
## can't update enum after create
>>> letters.a = 'x'
Traceback (most recent call last):
...
AttributeError: 'EnumClass' object attribute 'a' is read-only
## can't update enum after create
>>> del letters.u
Traceback (most recent call last):
...
AttributeError: 'EnumClass' object attribute 'u' is read-only
## can't have non-unique enum values
>>> x = enum('a','b','c','a')
Traceback (most recent call last):
...
AssertionError: Enums must not repeat values
## can't have zero enum values
>>> x = enum()
Traceback (most recent call last):
...
AssertionError: Empty enums are not supported
## can't have enum values that look like special function names
## since these could collide and lead to non-obvious errors
>>> x = enum('a','b','c','__cmp__')
Traceback (most recent call last):
...
AssertionError: Enum values beginning with __ are not supported
LIMITATIONS
Enum values of unicode type are not preserved, mapped to ASCII instead.
"""
## must have at least one enum value
assert names, 'Empty enums are not supported'
## enum values must be strings
assert len([i for i in names if not isinstance(i, types.StringTypes) and not \
isinstance(i, unicode)]) == 0, 'Enum values must be string or unicode'
## enum values must not collide with special function names
assert len([i for i in names if i.startswith("__")]) == 0,\
'Enum values beginning with __ are not supported'
## each enum value must be unique from all others
assert names == uniquify(names), 'Enums must not repeat values'
class EnumClass(object):
""" See parent function for explanation """
__slots__ = names
def __iter__(self):
return iter(constants)
def __len__(self):
return len(constants)
def __getitem__(self, i):
## this makes xx['name'] possible
if isinstance(i, types.StringTypes):
i = names.index(i)
## handles the more normal xx[0]
return constants[i]
def __repr__(self):
return 'enum' + str(names)
def __str__(self):
return 'enum ' + str(constants)
def index(self, i):
return names.index(i)
class EnumValue(object):
""" See parent function for explanation """
__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):
assert self.enumtype is other.enumtype, 'Only values from the same enum are comparable'
return cmp(self.value, other.value)
def __invert__(self):
return constants[maximum - self.value]
def __nonzero__(self):
## return bool(self.value)
## Original code led to bool(x[0])==False, not correct
return True
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