python - 具有 Python 属性的属性映射

Question

有没有办法让 Python @property 同时充当 setter 和 getter？

我觉得我以前在哪里见过这个，但不记得也无法自己重新创建解决方案。

例如，代替:

class A(object):
  def __init__(self, b): self.b = b
  def get_c(self): return self.b.c
  def set_c(self, value): self.b.c = value
  c = property(get_c, set_c)

我们可以以某种方式表示对于 A 对象，c 属性实际上等同于 b.c 的 getter、setter(和删除器，如果我们喜欢)。

动机:

当我们需要 A 作为 B 对象(其中 b 是一个实例)的代理包装器时，这将特别有用但是仅共享数据属性，不共享方法。诸如此类的属性将允许 A 和 B 对象的数据在同一代码使用时保持完全同步。

Answer 1

我想你在找this forwardTo class正如在 ActiveState 上发布的那样。

This recipe lets you transparently forward attribute access to another object in your class. This way, you can expose functionality from some member of your class instance directly, e.g. foo.baz() instead of foo.bar.baz().

class forwardTo(object):
    """
    A descriptor based recipe that makes it possible to write shorthands
    that forward attribute access from one object onto another.

    >>> class C(object):
    ...     def __init__(self):
    ...         class CC(object):
    ...             def xx(self, extra):
    ...                 return 100 + extra
    ...             foo = 42
    ...         self.cc = CC()
    ...
    ...     localcc = forwardTo('cc', 'xx')
    ...     localfoo = forwardTo('cc', 'foo')
    ...
    >>> print C().localcc(10)
    110
    >>> print C().localfoo
    42

    Arguments: objectName - name of the attribute containing the second object.
               attrName - name of the attribute in the second object.
    Returns:   An object that will forward any calls as described above.
    """
    def __init__(self, objectName, attrName):
        self.objectName = objectName
        self.attrName = attrName
    def __get__(self, instance, owner=None):
        return getattr(getattr(instance, self.objectName), self.attrName)
    def __set__(self, instance, value):
        setattr(getattr(instance, self.objectName), self.attrName, value)
    def __delete__(self, instance):
        delattr(getattr(instance, self.objectName), self.attrName)

为了获得更健壮的代码，您可能需要考虑将 getattr(instance, self.objectName) 替换为 operator.attrgetter(self.objectName)(instance)。这将允许 objectName 成为带点的名称(例如，您可以让 A.c 成为 A.x.y.z.d 的代理)。