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
Davidg建议使用词典。我想更进一步,使用集合:
months = set('January', 'February', ..., 'December')
现在你可以测试一个值是否与集合中的一个值匹配,如下所示:
if m in months:
但是,像dF,我通常只使用字符串常量来代替枚举。
其他回答
Python没有内置的enum,其他答案有实现自己的enum的想法(您可能也对Python烹饪书中的顶部版本感兴趣)。
然而,在C中调用枚举的情况下,我通常只使用简单的字符串:由于对象/属性的实现方式,(C)Python已经优化为使用短字符串工作得非常快,因此使用整数并没有任何性能上的好处。为了防止输入错误/无效值,可以在选定的位置插入检查。
ANIMALS = ['cat', 'dog', 'python']
def take_for_a_walk(animal):
assert animal in ANIMALS
...
(与使用类相比,一个缺点是您失去了自动完成的好处)
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'
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)
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()
枚举已按照PEP 435中的描述添加到Python 3.4。它还被反向移植到pypi上的3.3、3.2、3.1、2.7、2.6、2.5和2.4。
对于更高级的Enum技术,请尝试aenum库(2.7,3.3+,与enum34是同一作者)。py2和py3之间的代码并不完全兼容,例如,你需要在python 2中使用__order__)。
要使用enum34,执行$ pip install enum34 要使用aenum,执行$ pip install aenum
安装enum(没有编号)将安装一个完全不同且不兼容的版本。
from enum import Enum # for enum34, or the stdlib version
# from aenum import Enum # for the aenum version
Animal = Enum('Animal', 'ant bee cat dog')
Animal.ant # returns <Animal.ant: 1>
Animal['ant'] # returns <Animal.ant: 1> (string lookup)
Animal.ant.name # returns 'ant' (inverse lookup)
或者说:
class Animal(Enum):
ant = 1
bee = 2
cat = 3
dog = 4
在早期版本中,完成枚举的一种方法是:
def enum(**enums):
return type('Enum', (), enums)
是这样使用的:
>>> Numbers = enum(ONE=1, TWO=2, THREE='three')
>>> Numbers.ONE
1
>>> Numbers.TWO
2
>>> Numbers.THREE
'three'
你也可以很容易地支持自动枚举,就像这样:
def enum(*sequential, **named):
enums = dict(zip(sequential, range(len(sequential))), **named)
return type('Enum', (), enums)
并像这样使用:
>>> Numbers = enum('ZERO', 'ONE', 'TWO')
>>> Numbers.ZERO
0
>>> Numbers.ONE
1
支持将值转换回名称可以这样添加:
def enum(*sequential, **named):
enums = dict(zip(sequential, range(len(sequential))), **named)
reverse = dict((value, key) for key, value in enums.iteritems())
enums['reverse_mapping'] = reverse
return type('Enum', (), enums)
这将覆盖带有该名称的任何内容,但对于在输出中呈现枚举非常有用。如果反向映射不存在,它将抛出一个KeyError。第一个例子:
>>> Numbers.reverse_mapping['three']
'THREE'
如果你使用MyPy,另一种表达“枚举”的方式是typing.Literal。
例如:
from typing import Literal #python >=3.8
from typing_extensions import Literal #python 2.7, 3.4-3.7
Animal = Literal['ant', 'bee', 'cat', 'dog']
def hello_animal(animal: Animal):
print(f"hello {animal}")
hello_animal('rock') # error
hello_animal('bee') # passes