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                                    Python的高级语法与用法

一、枚举其实是一个类    

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4print(VIP.BLACK)运行结果：VIP.BLACK

二、枚举和普通类相比有什么优势

    1、普通类值可变，枚举值不可变；

    2、普通类变量名可相同，且值为最近的一个变量值，枚举变量名不可重复。   

from enum import Enumclass Common():    YELLOW = 1    YELLOW = 2print(Common.YELLOW)运行结果：2class VIP(Enum):    YELLOW = 1    YELLOW = 5    GREEN = 2    BLACK = 3    RED = 4    print(VIP.YELLOW.value)运行结果：Traceback (most recent call last):  File "/home/caoxuejin/Project/sample/chapter11/c1.py", line 17, in 
   
        class VIP(Enum):  File "/home/caoxuejin/Project/sample/chapter11/c1.py", line 19, in VIP    YELLOW = 5  File "/home/caoxuejin/myEnvs/python37/lib/python3.7/enum.py", line 100, in __setitem__    raise TypeError('Attempted to reuse key: %r' % key)TypeError: Attempted to reuse key: 'YELLOW'
   

三、枚举类型、枚举名称和枚举值

    1、枚举名称：

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4# 枚举名称print(VIP.YELLOW.name)运行结果：YELLOW

    2、枚举值：        

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4# 枚举值print(VIP.YELLOW.value)运行结果：1

    3、枚举类型：        

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4# 枚举类型print(VIP.YELLOW)运行结果：VIP.YELLOWprint(VIP["YELLOW"])运行结果：VIP.YELLOWprint(type(VIP.YELLOW))运行结果：
   

    4、枚举遍历：     

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4# 枚举遍历for v in VIP:    print(v)运行结果：VIP.YELLOWVIP.GREENVIP.BLACKVIP.RED

四、枚举的比较运算

    1、==：

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4class VIPS(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4result = (VIP.YELLOW==VIP.YELLOW)print(result)运行结果：Trueresult = (VIP.YELLOW==1)print(result)运行结果：Falseresult = (VIP.YELLOW==VIPS.YELLOW)print(result)运行结果：False

    2、is：    

from enum import Enumclass VIP(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4class VIPS(Enum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4result = (VIP.YELLOW is VIP.YELLOW)print(result)运行结果：Trueresult = (VIP.YELLOW is 1)print(result)运行结果：Falseresult = (VIP.YELLOW is VIPS.YELLOW)print(result)运行结果：False

五、枚举注意事项

    1、别名：当两个枚举的枚举值相同时，后一个枚举为前一个枚举的别名。        

from enum import Enumclass VIP(Enum):    YELLOW = 1    YELLOW_ALIAS = 1  # 别名    GREEN = 2    BLACK = 3    RED = 4print(VIP.YELLOW)运行结果：VIP.YELLOWprint(VIP.YELLOW_ALIAS)运行结果：VIP.YELLOWfor v in VIP:    print(v)运行结果：VIP.YELLOWVIP.GREENVIP.BLACKVIP.RED

    2、如若需要在遍历的时候把别名遍历出来，有如下两种方式：

        (1) 方式一：获取标签名及枚举类型

from enum import Enumclass VIP(Enum):    YELLOW = 1    YELLOW_ALIAS = 1    GREEN = 2    BLACK = 3    RED = 4for v in VIP.__members__.items():    print(v)运行结果：('YELLOW', 
   
    )('YELLOW_ALIAS', 
    
     )('GREEN', 
     
      )('BLACK', 
      
       )('RED', 
       
        )
       
      
     
    
   

        (2) 方式二：  获取标签名          

from enum import Enumclass VIP(Enum):    YELLOW = 1    YELLOW_ALIAS = 1    GREEN = 2    BLACK = 3    RED = 4for v in VIP.__members__:    print(v)运行结果：YELLOWYELLOW_ALIASGREENBLACKRED

六、枚举转换

from enum import Enumclass VIP(Enum):    YELLOW = 1    YELLOW_ALIAS = 1    GREEN = 2    BLACK = 3    RED = 4a = 1print(VIP(a))运行结果：VIP.YELLOW

七、枚举小结

    1、当引入父类的枚举类型为IntEnum时，枚举值必须为int类型    

from enum import Enum, IntEnumclass VIP(IntEnum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = "four"print(VIP.RED)运行结果：Traceback (most recent call last):  File "/home/caoxuejin/Project/sample/chapter11/c5.py", line 9, in 
   
        class VIP(IntEnum):  File "/home/caoxuejin/myEnvs/python37/lib/python3.7/enum.py", line 217, in __new__    enum_member = __new__(enum_class, *args)ValueError: invalid literal for int() with base 10: 'four'class VIP(IntEnum):    YELLOW = 1    GREEN = 2    BLACK = 3    RED = 4print(VIP.RED)运行结果：VIP.RED
   

    2、如若加了@unique装饰器的话，枚举值是不允许相同的

from enum import Enum, IntEnum, unique@uniqueclass VIP(IntEnum):    YELLOW = 1    GREEN = 1    BLACK = 3    RED = 4print(VIP.RED)运行结果：Traceback (most recent call last):  File "/home/caoxuejin/Project/sample/chapter11/c5.py", line 10, in 
   
        class VIP(IntEnum):  File "/home/caoxuejin/myEnvs/python37/lib/python3.7/enum.py", line 848, in unique    (enumeration, alias_details))ValueError: duplicate values found in 
    
     : GREEN -> YELLOW
    
   

九、什么是闭包

    1、闭包：在函数嵌套的程序结构中，如果内层函数包含对外层函数局部变量的引用，同时外层函数的返回结果又是对内层函数的引用，这就构成了一个闭包。

    2、示例：

        (1) 示例一：闭包            

def cure_pre():    a = 25    def cure(x):        return a*x*x    return curea = 10f = cure_pre()print(f.__closure__)print(f.__closure__[0].cell_contents)print(f(2))运行结果：(
   
    ,)25100
   

        (2) 示例二：非闭包            

a = 25def cure_pre():    def cure(x):        return a*x*x    return curea = 10f = cure_pre()print(f(2))运行结果：40

十一、一个示例看看闭包

def f1():    a = 10    def f2():        a = 20        print(a)    print(a)    f2()    print(a)f1()运行结果：102010

十二、闭包的经典误区

    1、正确：    

def f1():    a = 10    def f2():        # a被python认为是一个局部变量        # a = 25        c = 20 * a        return c    return f2f = f1()print(f)print(f.__closure__)print(f.__closure__[0].cell_contents)运行结果：
   
    .f2 at 0x7fe9ca018d90>(
    
     ,)10
    
   

    2、错误：

def f1():    a = 10    def f2():        # a被python认为是一个局部变量        a = 25        c = 20 * a        return c    return f2f = f1()print(f)print(f.__closure__)print(f.__closure__[0].cell_contents)运行结果：
   
    .f2 at 0x7f6f56b85d90>None  File "/home/caoxuejin/Project/sample/chapter11/c9.py", line 21, in 
    
         print(f.__closure__[0].cell_contents)
    
   

十三、闭包示例

    1、非闭包方式：

origin = 0def go(step):    global origin    new_pos = origin + step    origin = new_pos    return originprint(go(2))print(go(3))print(go(6))运行结果：2511

    2、闭包方式：    

origin = 0def factory(pos):    def go(step):        nonlocal pos        new_pos = pos + step        pos = new_pos        return pos    return gotourist = factory(origin)print(tourist(2))print(tourist.__closure__[0].cell_contents)print(tourist(3))print(tourist.__closure__[0].cell_contents)print(tourist(6))print(tourist.__closure__[0].cell_contents)运行结果：22551111