python 类装饰器与元类

类装饰器，元类

还有一些技术可以简化上面的代码，其中一种是使用类装饰器：

Class decorator to apply constraints

def check_attributes(**kwargs): def decorate(cls): for key, value in kwargs.items(): if isinstance(value, Descriptor): value.name = key setattr(cls, key, value) else: setattr(cls, key, value(key)) return cls

return decorate

Example

@check_attributes(name=SizedString(size=8), shares=UnsignedInteger, price=UnsignedFloat) class Stock: def init(self, name, shares, price): self.name = name self.shares = shares self.price = price 另外一种方式是使用元类：

A metaclass that applies checking

class checkedmeta(type): def new(cls, clsname, bases, methods): # Attach attribute names to the descriptors for key, value in methods.items(): if isinstance(value, Descriptor): value.name = key return type.new(cls, clsname, bases, methods)

Example

class Stock2(metaclass=checkedmeta): name = SizedString(size=8) shares = UnsignedInteger() price = UnsignedFloat()

def __init__(self, name, shares, price):
    self.name = name
    self.shares = shares
    self.price = price