Python类的高级主题 - littleboy12580/learning_python GitHub Wiki

类的高级主题

slots

Python在定义class的时候，可以通过定义一个特殊的__slots__变量，来限制该class实例能添加的属性

class Student(object):
    __slots__ = ('name', 'age') # 用tuple定义允许绑定的属性名称
s = Student() # 创建新的实例
s.name = 'Michael' # 绑定属性'name'
s.age = 25 # 绑定属性'age'
s.score = 99 # 绑定属性'score'

在绑定score时会报错

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Student' object has no attribute 'score'

slots__定义的属性仅对当前类实例起作用，对继承的子类是不起作用的，除非在子类中也定义__slots，此时子类实例允许定义的属性就是自身的__slots__加上父类的__slots__。

枚举类

from enum import Enum
Month = Enum('Month', ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'))
for name, member in Month.__members__.items():
    print(name, '=>', member, ',', member.value)

其中name是类中成员名，member则是成员全称名（类名加成员名），value属性是自动赋给成员的int常量，默认从1开始计数

如果需要更精确地控制枚举类型，可以从Enum派生出自定义类：

from enum import Enum, unique
class Weekday(Enum):
    Sun = 0 # Sun的value被设定为0
    Mon = 1
    Tue = 2
    Wed = 3
    Thu = 4
    Fri = 5
    Sat = 6
for name, member in Weekday.__members__.items():
    print(name, '=>', member)

输出结果为

Sun => Weekday.Sun
Mon => Weekday.Mon
Tue => Weekday.Tue
Wed => Weekday.Wed
Thu => Weekday.Thu
Fri => Weekday.Fri
Sat => Weekday.Sat
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