How to implement enumeration in Python

Use ordinary classes to directly implement enumerations

In Python, enumerations are the same as the class variables we define in objects. Each class variable is an enumeration item. , the way to access enumeration items is: class name plus class variable, like the following:

class color():
    YELLOW  = 1
    RED     = 2
    GREEN   = 3
    PINK    = 4
 
# 访问枚举项
print(color.YELLOW) # 1

Although this can solve the problem, it is not rigorous and not very safe, such as:

1. In an enumeration class, there should be no enumeration items (class variables) with the same key.

2. It is not allowed to modify the value of the enumeration item directly outside the class.

class color():
    YELLOW  = 1
    YELLOW  = 3   # 注意这里又将YELLOW赋值为3，会覆盖前面的1
    RED     = 2
    GREEN   = 3
    PINK    = 4
 
# 访问枚举项
print(color.YELLOW) # 3
 
# 但是可以在外部修改定义的枚举项的值，这是不应该发生的
color.YELLOW = 99
print(color.YELLOW) # 99

Solution: Use enum module

The enum module is a built-in module in the system and can be imported directly using import. However, when importing, it is not recommended to use import enum to transfer all the data in the enum module. Import, generally the most commonly used ones are Enum, IntEnum, and unique in the enum module

# 导入枚举类
from enum import Enum
 
# 继承枚举类
class color(Enum):
    YELLOW  = 1
    BEOWN   = 1 
    # 注意BROWN的值和YELLOW的值相同，这是允许的，此时的BROWN相当于YELLOW的别名
    RED     = 2
    GREEN   = 3
    PINK    = 4
 
class color2(Enum):
    YELLOW  = 1
    RED     = 2
    GREEN   = 3
    PINK    = 4

Use your own defined enumeration class:

print(color.YELLOW) # color.YELLOW
print(type(color.YELLOW)) # <enum &#39;color&#39;>
 
print(color.YELLOW.value)  # 1
print(type(color.YELLOW.value)) # <class &#39;int&#39;>
 
print(color.YELLOW == 1)    # False
print(color.YELLOW.value == 1)  # True
print(color.YELLOW == color.YELLOW)  # True
print(color.YELLOW == color2.YELLOW)  # False
print(color.YELLOW is color2.YELLOW)  # False
print(color.YELLOW is color.YELLOW)  # True
 
print(color(1))         # color.YELLOW
print(type(color(1)))   # <enum &#39;color&#39;>
　　注意事项如下：

1. Enumeration classes cannot be used Instantiate the object

2. To access an item in the enumeration class, just use the class name to access directly plus the item to be accessed, such as color.YELLOW

3. Enumeration class The Key = Value defined inside cannot be modified outside the class, which means that the following approach is wrong

color.YELLOW = 2  # Wrong, can't reassign member

4. Enumeration items can be used for comparison, using ==, or is　

5. After importing Enum, the Key and Value in an enumeration class cannot be the same. The values ​​can be the same, but the keys with the same value will be used as aliases.

6. If you want to enumerate the class The Value in can only be an integer number, then you can import IntEnum and then inherit IntEnum. Note that at this time, if the value is a string number, no error will be reported:

from enum import IntEnum

7. If If the keys in the enumeration class cannot be the same, then when importing Enum, you need to import the unique function

from enum import Enum, unique

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