python 高级语法与用法-枚举的简单用法

1、枚举

• 可读性更强

from enum import Enum

class VIP(Enum):
    YELLOW = 1
    GREEN  = 2
    BALCK  = 3
    RED    = 4

print(VIP.BALCK)
print(type(VIP.BALCK))
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
# VIP.BALCK
# <enum 'VIP'>

按照普通类来分析，类名.类变量 ，应该输出的是3，但是其实却是VIP.BALCK。

先不解释为什么。先说说，其实这种打印结果应该对调用该类的业务方来说，是更希望看到VIP.BALCK的吧，而不是一个数字3，也不知道这个意义是啥。

这就是说，枚举类不能按照普通类来分析。

接下来说说枚举类的特点和优势

• 枚举类中的value不可变:Cannot reassign members；业务需求中，往往也需要定义的常量类型，是不允许被修改的。

• from enum import Enum
  
  class VIP(Enum):
      YELLOW = 1
      GREEN  = 1
      BALCK  = 3
      RED    = 4
  
  print(VIP.GREEN)
  VIP.GREEN = 5
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
  # VIP.GREEN
  # Traceback (most recent call last):
  #   File "/Users/anson/Documents/Project/python_ToolCodes/test17.py", line 10, in <module>
  #     VIP.GREEN = 5
  #   File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/enum/__init__.py", line 419, in __setattr__
  #     raise AttributeError('Cannot reassign members.')
  # AttributeError: Cannot reassign members.
  
  用普通类代替枚举类，被轻易修改
  

  class Common():
      GREEN = 1
  Common.GREEN = 3
  print(Common.GREEN)
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
  # 3

  dict来替代枚举类，被轻易修改

  a = {"GREEN":1,"RED":4}
  a["GREEN"] = 3
  print(a)
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
  # {'GREEN': 3, 'RED': 4}

   

• 枚举类中不能存在相同的标签名

• from enum import Enum
  
  class Animal(Enum):
      CAT = 1
      CAT = 2
  # anson@ansonwandeMacBook-Pro python_ToolCodes % python3 test19.py 
  # Traceback (most recent call last):
  #   File "test19.py", line 3, in <module>
  #     class Animal(Enum):
  #   File "test19.py", line 5, in Animal
  #     CAT = 2
  #   File "/usr/local/Cellar/python@3.8/3.8.3_2/Frameworks/Python.framework/Versions/3.8/lib/python3.8/enum.py", line 95, in __setitem__
  #     raise TypeError('Attempted to reuse key: %r' % key)
  # TypeError: Attempted to reuse key: 'CAT'

  需要注意的是，python2.7版本是允许有相同名称的标签的，但是目前所学的python3.8时不允许有相同名称的标签的

• 获取枚举的标签和数值，该怎么操作VIP.YELLOW.name,VIP.YELLOW.value

• from enum import Enum
  #coding=utf-8
  
  class VIP(Enum):
      YELLOW = 1
      GRAY   = 2
      BALCK  = 3
      RED    = 4
  print(VIP.YELLOW)
  print(VIP.YELLOW.name)
  print(VIP.YELLOW.value)
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
  # VIP.YELLOW
  # YELLOW
  # 1

   

• 枚举遍历

  from enum import Enum
  #coding=utf-8
  
  class VIP(Enum):
      YELLOW = 1
      GRAY   = 2
      BALCK  = 3
      RED    = 4
  for v in VIP:
      print(v)
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
  # VIP.YELLOW
  # VIP.GRAY
  # VIP.BALCK
  # VIP.RED

   

• 枚举比较

  • “==”比较：允许
    

    from enum import Enum
    #coding=utf-8
    
    class VIP(Enum):
        YELLOW = 1
        GRAY   = 2
        BALCK  = 3
        RED    = 4
    print(VIP.BALCK == VIP.GRAY)
    # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
    # False

    
    >,<比较：不允许！！！
    

    from enum import Enum
    #coding=utf-8
    
    class VIP(Enum):
        YELLOW = 1
        GRAY   = 2
        BALCK  = 3
        RED    = 4
    print(VIP.BALCK > VIP.GRAY)
    # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
    # Traceback (most recent call last):
    #   File "/Users/anson/Documents/Project/python_ToolCodes/test17.py", line 9, in <module>
    #     print(VIP.BALCK > VIP.GRAY)
    #   File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/enum/__init__.py", line 740, in __gt__
    #     raise TypeError("unorderable types: %s() > %s()" % (self.__class__.__name__, other.__class__.__name__))
    # TypeError: unorderable types: VIP() > VIP()

    
    is 比较：允许

    from enum import Enum
    #coding=utf-8
    
    class VIP(Enum):
        YELLOW = 1
        GRAY   = 2
        BALCK  = 3
        RED    = 4
    print(VIP.BALCK is VIP.BALCK)
    # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
    # True

    枚举类之间比较：允许
    

    from enum import Enum
    #coding=utf-8
    
    class VIP1(Enum):
        YELLOW = 1
        GRAY   = 2
        BALCK  = 3
        RED    = 4
    
    class VIP2(Enum):
        YELLOW = 1
        GRAY   = 2
        BALCK  = 3
        RED    = 4
    print(VIP1.GRAY is VIP2.GRAY)
    # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test17.py"
    # False

 

• 枚举类型转换

• 值转为枚举标签
  from enum import Enum
  
  class Animal(Enum):
      CAT = 1
      DOG = 2
  
  a = 1
  print(Animal(a))
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test19.py"
  # Animal.CAT

   

• 枚举小结

  1、IntEunm 与Enum 的区别是，IntEum 至于许标签值是Int的,float　　
  
  from enum import IntEnum
  
  class Animal(IntEnum):
      CAT = 'sss'
      DOG = 2
  
  a = 1
  print(Animal(a))
  Traceback (most recent call last):
    File "test19.py", line 3, in <module>
      class Animal(IntEnum):
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/enum/__init__.py", line 230, in __new__
      enum_member = __new__(enum_class, *args)
  ValueError: invalid literal for int() with base 10: 'sss'

  2、枚举的标签是不允许重复的，但是枚举的值是可以重复的，然而开发时，往往是不需要重复的，这时候，我们可以用装饰器
  @unique来限制枚举的值不能重复
  from enum import Enum,unique
  @unique
  class Animal(Enum):
      CAT = 1
      DOG = 1
  
  a = 1
  print(Animal(a))
  
  # anson@ansonwandeMacBook-Pro python_ToolCodes % python3  test19.py
  # Traceback (most recent call last):
  #   File "test19.py", line 3, in <module>
  #     class Animal(Enum):
  #   File "/usr/local/Cellar/python@3.8/3.8.3_2/Frameworks/Python.framework/Versions/3.8/lib/python3.8/enum.py", line 860, in unique
  #     raise ValueError('duplicate values found in %r: %s' %
  # ValueError: duplicate values found in <enum 'Animal'>: DOG -> CAT