Question

Python 3.4.0介绍enum，我已经阅读doc但仍然不知道它的用法。从我的角度来看，枚举是一种扩展的namedtuple类型，可能不是真的。所以这些是我想知道的枚举：

使用枚举的时间和地点？
为什么我们需要枚举？有什么好处？
究竟是什么？

Answer 1

1。何时何地使用枚举？

如果您的变量采用了一组有限的可能值。

例如，一周中的几天：

class Weekday(Enum):
    MONDAY = 1
    TUESDAY = 2
    WEDNESDAY = 3
    THURSDAY = 4
    FRIDAY = 5
    SATURDAY = 6
    SUNDAY = 7

2。为什么我们需要枚举？有什么好处？

枚举是有利的，因为它们为常量命名，使代码更具可读性;并且因为个别成员无法反弹，使得Python Enums半常数（因为Enum本身仍然可以反弹）。
除了更易读的代码外，调试也更容易，因为您会看到名称和值，而不仅仅是值
可以将所需行为添加到枚举

例如，正如使用datetime模块的任何人都知道的那样，datetime和date对一周中的几天有两种不同的重复：0-6或1-7 。我们可以在Weekday枚举中添加一个方法，以便从datetime或date实例中提取日期并返回匹配的枚举成员，而不是跟踪自己：

    @classmethod
    def from_date(cls, date):
        return cls(date.isoweekday())

3。究竟究竟是什么？

枚举是type，其成员名为常量，它们都属于（或应该）逻辑值组。到目前为止，我已经创建了Enum s：
```
- the days of the week
- the months of the year
- US Federal Holidays in a year
```

FederalHoliday是我最复杂的;它使用this recipe，并且有方法可以返回给定年份假日发生的实际日期，如果有问题的日子是假日，则返回下一个工作日（或者跳过的天数包括假日或周末）），以及一年的完整日期。这是：

class FederalHoliday(AutoEnum):
    NewYear = "First day of the year.", 'absolute', Month.JANUARY, 1
    MartinLutherKingJr = "Birth of Civil Rights leader.", 'relative', Month.JANUARY, Weekday.MONDAY, 3
    President = "Birth of George Washington", 'relative', Month.FEBRUARY, Weekday.MONDAY, 3
    Memorial = "Memory of fallen soldiers", 'relative', Month.MAY, Weekday.MONDAY, 5
    Independence = "Declaration of Independence", 'absolute', Month.JULY, 4
    Labor = "American Labor Movement", 'relative', Month.SEPTEMBER, Weekday.MONDAY, 1
    Columbus = "Americas discovered", 'relative', Month.OCTOBER, Weekday.MONDAY, 2
    Veterans = "Recognition of Armed Forces service", 'relative', Month.NOVEMBER, 11, 1
    Thanksgiving = "Day of Thanks", 'relative', Month.NOVEMBER, Weekday.THURSDAY, 4
    Christmas = "Birth of Jesus Christ", 'absolute', Month.DECEMBER, 25

    def __init__(self, doc, type, month, day, occurance=None):
        self.__doc__ = doc
        self.type = type
        self.month = month
        self.day = day
        self.occurance = occurance

    def date(self, year):
        "returns the observed date of the holiday for `year`"
        if self.type == 'absolute' or isinstance(self.day, int):
            holiday =  Date(year, self.month, self.day)
            if Weekday(holiday.isoweekday()) is Weekday.SUNDAY:
                holiday = holiday.replace(delta_day=1)
            return holiday
        days_in_month = days_per_month(year)
        target_end = self.occurance * 7 + 1
        if target_end > days_in_month[self.month]:
            target_end = days_in_month[self.month]
        target_start = target_end - 7
        target_week = list(xrange(start=Date(year, self.month, target_start), step=one_day, count=7))
        for holiday in target_week:
            if Weekday(holiday.isoweekday()) is self.day:
                return holiday

    @classmethod
    def next_business_day(cls, date, days=1):
        """
        Return the next `days` business day from date.
        """
        holidays = cls.year(date.year)
        years = set([date.year])
        while days > 0:
            date = date.replace(delta_day=1)
            if date.year not in years:
                holidays.extend(cls.year(date.year))
                years.add(date.year)
            if Weekday(date.isoweekday()) in (Weekday.SATURDAY, Weekday.SUNDAY) or date in holidays:
                continue
            days -= 1
        return date

    @classmethod
    def year(cls, year):
        """
        Return a list of the actual FederalHoliday dates for `year`.
        """
        holidays = []
        for fh in cls:
            holidays.append(fh.date(year))
        return holidays

备注：

Date来自my dbf package

增强型xrange（支持一系列日期）也是自定义的，但我认为我没有把它包含在任何地方;下次我修补它时，我会将它填入我的dbf包中。

披露：我是Python stdlib Enum，enum34 backport和Advanced Enumeration (aenum)图书馆的作者。

Answer 2

在Python中引入Enum背后的

PEP 435 ("Adding an Enum type to the Python standard library")有很多examples作者希望如何使用它。

更多评论here。

Python枚举，何时何地使用？

2 个答案: