[Python] How to get a value with a key other than value with Enum

How to get a value with a key other than value with Enum

Introduction

Many programming languages have an Enum. It's in Python as well. To get a member, you can get each value as a key, but you cannot get any other value as a key. I will introduce it because it was possible by extending the normal Enum.

Normal Enum confirmation

First, let's check how to use Enum normally.

>>> from enum import Enum
>>>
>>> class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 3

#If you declare an Enum as above
#You can access each member by using a value such as 1 or 2 as a key.

>>> color = Color(1)
>>> print(color)
Color.RED

#Of course you can also access it directly
>>> print(Color.RED)
Color.RED
>>> print(color == Color.RED)
True

Thing you want to do

You could access Color.RED withColor (1), but if you can access withColor ('red')andColor ('red')for example, the possibilities of ʻEnum` will expand.

>>> from enum import Enum
>>>
>>> class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 3

#Of course I get an error when I try to access as below
>>> color = Color('red')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.6/enum.py", line 293, in __call__
    return cls.__new__(cls, value)
  File "/usr/local/lib/python3.6/enum.py", line 535, in __new__
    return cls._missing_(value)
  File "/usr/local/lib/python3.6/enum.py", line 548, in _missing_
    raise ValueError("%r is not a valid %s" % (value, cls.__name__))
ValueError: 'red' is not a valid Color

>>> color = Color('Red')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.6/enum.py", line 293, in __call__
    return cls.__new__(cls, value)
  File "/usr/local/lib/python3.6/enum.py", line 535, in __new__
    return cls._missing_(value)
  File "/usr/local/lib/python3.6/enum.py", line 548, in _missing_
    raise ValueError("%r is not a valid %s" % (value, cls.__name__))
ValueError: 'Red' is not a valid Color

Implementation

Now let's check the implementation of Enum that extends key.

#At the time of declaration as follows`_value2member_map_`To update
>>> from enum import Enum
>>>
>>> class Color(Enum):
...     def __new__(cls, value, en, ja):
...         obj = object.__new__(cls)
...         obj._value_ = value
...         cls._value2member_map_.update({en: obj, ja: obj})
...         return obj
...     RED = (1, 'red', 'Red')
...     GREEN = (2, 'green', 'Green')
...     BLUE = (3, 'blue', 'Blue')

#With this as before'red'Or'Red'When you access with
>>> color = Color('red')
>>> print(color)
Color.RED

>>> red = Color('Red')
>>> print(red)
Color.RED

Finally

If you overdo it, the key may be worn, but I think it's worth knowing. It seems that it can be used with int type in DB and str type in API.