python - 如何使用将名称列表作为参数的装饰器向类添加属性？

Question

我想通过装饰器向类添加许多虚拟属性，如下所示:

def addAttrs(attr_names):
  def deco(cls):
    for attr_name in attr_names:
      def getAttr(self):
        return getattr(self, "_" + attr_name)
      def setAttr(self, value):
        setattr(self, "_" + attr_name, value)
      prop = property(getAttr, setAttr)
      setattr(cls, attr_name, prop)
      setattr(cls, "_" + attr_name, None) # Default value for that attribute
    return cls
  return deco

@addAttrs(['x', 'y'])
class MyClass(object):
  pass

不幸的是，decoarator 似乎保留了 attr_name 的引用而不是它的内容。因此，MyClass.x 和 MyClass.y 都访问 MyClass._y:

a = MyClass()
a.x = 5
print a._x, a._y
>>> None, 5
a.y = 8
print a._x, a._y
>>> None, 8

我必须更改什么才能获得预期的行为？

Answer 1

您几乎成功了。只有一个尼特。创建内部函数时，将 attr_name 的当前值绑定(bind)到 getter 和 setter 函数中:

def addAttrs(attr_names):
  def deco(cls):
    for attr_name in attr_names:
      def getAttr(self, attr_name=attr_name):
        return getattr(self, "_" + attr_name)
      def setAttr(self, value, attr_name=attr_name):
        setattr(self, "_" + attr_name, value)
      prop = property(getAttr, setAttr)
      setattr(cls, attr_name, prop)
      setattr(cls, "_" + attr_name, None) # Default value for that attribute
    return cls
  return deco

@addAttrs(['x', 'y'])
class MyClass(object):
  pass

这会产生预期的结果:

>>> a = MyClass()
>>> a.x = 5
>>> print a._x, a._y
5 None
>>> a.y = 8
>>> print a._x, a._y
5 8

希望这对您有所帮助。装饰愉快:-)