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Python 3.4.0 引入enum，我已经阅读了文档但仍然不知道它的用法。从我的角度来看，enum.Enum是一个扩展namedtuple类型，这可能不是真的。所以这些是我想知道的Enum：

  1. 何时何地使用Enum？
  2. 为什么我们需要Enum？有什么优势？
  3. 究竟是什么Enum？
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1 回答 1

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1. 何时何地使用枚举？

  • 当您有一个变量采用一组有限的可能值中的一个时。

例如，星期几：

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？有什么优势？

  • 枚举是有利的，因为它们为常量命名，这使代码更具可读性；并且因为单个成员不能被反弹，使得 Python Enums 是半常量（因为它Enum本身仍然可以被反弹）。

  • 除了更具可读性的代码之外，调试也更容易，因为您可以看到名称和值，而不仅仅是值

  • 可以将所需的行为添加到 Enums

例如，任何使用过datetime模块的人都知道，datetime并且date有两种不同的表示星期几：0-6 或 1-7。我们可以向枚举添加一个方法来从or实例Weekday中提取日期并返回匹配的枚举成员，而不是自己跟踪它：datetimedate

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

3. Enum 到底是什么？

  • Enum 是一种类型，其成员被命名为常量，它们都属于（或应该）一个逻辑值组。到目前为止，我已经Enum为：

    - the days of the week
- the months of the year
- US Federal Holidays in a year

FederalHoliday是我最复杂的；它使用这个配方，并有方法返回给定年份的假期实际发生日期，如果相关日期是假期则返回下一个工作日（或跳过的天数范围包括假期或周末），以及一年的完整日期集。这里是：

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, occurrence=None):
        self.__doc__ = doc
        self.type = type
        self.month = month
        self.day = day
        self.occurrence = occurrence

    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.occurrence * 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：

于 2014-03-23T17:26:51.737 回答