如何在python中将int转换为Enum?

问题:如何在python中将int转换为Enum?

在python 2.7.6中使用新的Enum功能(通过backport enum34)。

给定以下定义,如何将int转换为相应的Enum值?

from enum import Enum

class Fruit(Enum):
    Apple = 4
    Orange = 5
    Pear = 6

我知道我可以手工制作一系列的if语句来进行转换,但是有没有简单的pythonic转换方法?基本上,我想要一个返回枚举值的函数ConvertIntToFruit(int)。

我的用例是我有一个记录的csv文件,在其中我将每个记录读入一个对象。文件字段之一是代表枚举的整数字段。在填充对象时,我想将文件中的整数字段转换为对象中对应的Enum值。

Using the new Enum feature (via backport enum34) with python 2.7.6.

Given the following definition, how can I convert an int to the corresponding Enum value?

from enum import Enum

class Fruit(Enum):
    Apple = 4
    Orange = 5
    Pear = 6

I know I can hand craft a series of if-statements to do the conversion but is there an easy pythonic way to convert? Basically, I’d like a function ConvertIntToFruit(int) that returns an enum value.

My use case is I have a csv file of records where I’m reading each record into an object. One of the file fields is an integer field that represents an enumeration. As I’m populating the object I’d like to convert that integer field from the file into the corresponding Enum value in the object.


回答 0

您“打电话”Enum上课:

Fruit(5)

轮到5Fruit.Orange

>>> from enum import Enum
>>> class Fruit(Enum):
...     Apple = 4
...     Orange = 5
...     Pear = 6
... 
>>> Fruit(5)
<Fruit.Orange: 5>

从文档的程序访问到枚举成员及其属性部分:

有时,以编程方式访问枚举中的成员很有用(例如,Color.red由于在编写程序时尚不知道确切的颜色而无法这样做)。Enum允许这样的访问:

>>> Color(1)
<Color.red: 1>
>>> Color(3)
<Color.blue: 3>

在相关说明中:要映射包含枚举成员名称的字符串值,请使用subscription:

>>> s = 'Apple'
>>> Fruit[s]
<Fruit.Apple: 4>

You ‘call’ the Enum class:

Fruit(5)

to turn 5 into Fruit.Orange:

>>> from enum import Enum
>>> class Fruit(Enum):
...     Apple = 4
...     Orange = 5
...     Pear = 6
... 
>>> Fruit(5)
<Fruit.Orange: 5>

From the Programmatic access to enumeration members and their attributes section of the documentation:

Sometimes it’s useful to access members in enumerations programmatically (i.e. situations where Color.red won’t do because the exact color is not known at program-writing time). Enum allows such access:

>>> Color(1)
<Color.red: 1>
>>> Color(3)
<Color.blue: 3>

In a related note: to map a string value containing the name of an enum member, use subscription:

>>> s = 'Apple'
>>> Fruit[s]
<Fruit.Apple: 4>

回答 1

我认为这是简单的话是对转换int价值为Enum通过调用EnumType(int_value),访问后name的的Enum对象:

my_fruit_from_int = Fruit(5) #convert to int
fruit_name = my_fruit_from_int.name #get the name
print(fruit_name) #Orange will be printed here

或作为功能:

def convert_int_to_fruit(int_value):
    try:
        my_fruit_from_int = Fruit(int_value)
        return my_fruit_from_int.name
    except:
        return None

I think it is in simple words is to convert the int value into Enum by calling EnumType(int_value), after that access the name of the Enum object:

my_fruit_from_int = Fruit(5) #convert to int
fruit_name = my_fruit_from_int.name #get the name
print(fruit_name) #Orange will be printed here

Or as a function:

def convert_int_to_fruit(int_value):
    try:
        my_fruit_from_int = Fruit(int_value)
        return my_fruit_from_int.name
    except:
        return None

回答 2

我想要类似的东西,以便可以从单个引用访问值对的任何一部分。香草版本:

#!/usr/bin/env python3


from enum import IntEnum


class EnumDemo(IntEnum):
    ENUM_ZERO       = 0
    ENUM_ONE        = 1
    ENUM_TWO        = 2
    ENUM_THREE      = 3
    ENUM_INVALID    = 4


#endclass.


print('Passes')
print('1) %d'%(EnumDemo['ENUM_TWO']))
print('2) %s'%(EnumDemo['ENUM_TWO']))
print('3) %s'%(EnumDemo.ENUM_TWO.name))
print('4) %d'%(EnumDemo.ENUM_TWO))
print()


print('Fails')
print('1) %d'%(EnumDemo.ENUM_TWOa))

失败将引发异常。

一个更强大的版本:

#!/usr/bin/env python3


class EnumDemo():


    enumeration =   (
                        'ENUM_ZERO',    # 0.
                        'ENUM_ONE',     # 1.
                        'ENUM_TWO',     # 2.
                        'ENUM_THREE',   # 3.
                        'ENUM_INVALID'  # 4.
                    )


    def name(self, val):
        try:

            name = self.enumeration[val]
        except IndexError:

            # Always return last tuple.
            name = self.enumeration[len(self.enumeration) - 1]

        return name


    def number(self, val):
        try:

            index = self.enumeration.index(val)
        except (TypeError, ValueError):

            # Always return last tuple.
            index = (len(self.enumeration) - 1)

        return index


#endclass.


print('Passes')
print('1) %d'%(EnumDemo().number('ENUM_TWO')))
print('2) %s'%(EnumDemo().number('ENUM_TWO')))
print('3) %s'%(EnumDemo().name(1)))
print('4) %s'%(EnumDemo().enumeration[1]))
print()
print('Fails')
print('1) %d'%(EnumDemo().number('ENUM_THREEa')))
print('2) %s'%(EnumDemo().number('ENUM_THREEa')))
print('3) %s'%(EnumDemo().name(11)))
print('4) %s'%(EnumDemo().enumeration[-1]))

如果使用不正确,这可以避免产生异常,而是传回故障指示。一种更Python化的方法是返回“ None”,但是我的特定应用程序直接使用文本。

I wanted something similar so that I could access either part of the value pair from a single reference. The vanilla version:

#!/usr/bin/env python3


from enum import IntEnum


class EnumDemo(IntEnum):
    ENUM_ZERO       = 0
    ENUM_ONE        = 1
    ENUM_TWO        = 2
    ENUM_THREE      = 3
    ENUM_INVALID    = 4


#endclass.


print('Passes')
print('1) %d'%(EnumDemo['ENUM_TWO']))
print('2) %s'%(EnumDemo['ENUM_TWO']))
print('3) %s'%(EnumDemo.ENUM_TWO.name))
print('4) %d'%(EnumDemo.ENUM_TWO))
print()


print('Fails')
print('1) %d'%(EnumDemo.ENUM_TWOa))

The failure throws an exception as would be expected.

A more robust version:

#!/usr/bin/env python3


class EnumDemo():


    enumeration =   (
                        'ENUM_ZERO',    # 0.
                        'ENUM_ONE',     # 1.
                        'ENUM_TWO',     # 2.
                        'ENUM_THREE',   # 3.
                        'ENUM_INVALID'  # 4.
                    )


    def name(self, val):
        try:

            name = self.enumeration[val]
        except IndexError:

            # Always return last tuple.
            name = self.enumeration[len(self.enumeration) - 1]

        return name


    def number(self, val):
        try:

            index = self.enumeration.index(val)
        except (TypeError, ValueError):

            # Always return last tuple.
            index = (len(self.enumeration) - 1)

        return index


#endclass.


print('Passes')
print('1) %d'%(EnumDemo().number('ENUM_TWO')))
print('2) %s'%(EnumDemo().number('ENUM_TWO')))
print('3) %s'%(EnumDemo().name(1)))
print('4) %s'%(EnumDemo().enumeration[1]))
print()
print('Fails')
print('1) %d'%(EnumDemo().number('ENUM_THREEa')))
print('2) %s'%(EnumDemo().number('ENUM_THREEa')))
print('3) %s'%(EnumDemo().name(11)))
print('4) %s'%(EnumDemo().enumeration[-1]))

When not used correctly this avoids creating an exception and, instead, passes back a fault indication. A more Pythonic way to do this would be to pass back “None” but my particular application uses the text directly.