Python递归__getattribute__

Question

我需要实现这样的行为：

obj.attr1.attr2.attr3 --> obj.attr1__attr2__attr3

看起来我必须覆盖obj的类__getattribute__，并以某种方式使用python描述符。

更新

我有一个django项目。

obj是django-haystack的SearchResult实例，它包含来自django模型的大量非规范化数据（user__name，user__address），我需要将其作为result.user.name访问兼容性原因。

更新THC4k的答案：

如果我有：

class Target(object):
    attr1 = 1
    attr1__attr2__attr3 = 5

>>> proxy.attr1
1
>>> proxy.attr1.attr2.attr3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'attr2'

非常感谢任何帮助。

Answer 1

我希望您知道自己在做什么，这不仅仅是避免修复现有代码的方案。

我认为有合理的理由这样做，毕竟我已经在Lua中做了类似的事情来实现一些C代码的包装，而不必为每个公开的函数实际编写代码。

但是你应该至少将实际的类与代理分开：

# the proxy maps attribute access to another object
class GetattrProxy(object):
    def __init__(self, proxied, prefix=None):
        self.proxied = proxied
        self.prefix = prefix

    def __getattr__(self, key):
        attr = (key if self.prefix is None else self.prefix + '__' + key)
        try:
            # if the proxied object has the attr return it
            return getattr(self.proxied, attr)
        except AttributeError:
            # else just return another proxy
            return GetattrProxy(self.proxied, attr)


# the thing you want to wrap
class Target(object):
    attr1__attr2__attr3 = 5


t = Target()
proxy = GetattrProxy(t)

print proxy.attr1.attr2.attr3

@katrielalex建议：

class GetattrProxy2(GetattrProxy):
    def __getattr__(self, key):
            attr = (key if self.prefix is None else self.prefix + '__' + key)
            proxy = GetattrProxy2(self.proxied, attr)

            # store val only if the proxied object has the attribute, 
            # this way we still get AttributeErrors on nonexisting items 
            if hasattr(self.proxied, attr):
                proxy.val = getattr(self.proxied, attr)
            return proxy

proxy = GetattrProxy2(t)
proxy.attr1.val # 1
proxy.attr1.attr2.attr3.val # 5
proxy.attr1.attr2.val # raise AttributeError

Answer 2

对于您拥有属性名称列表的情况，您可以使用itertools()函数（在python-3.x functools.reduce()中）和getattr()内置函数：

以下是一个例子：

In [1]: class A:
   ...:     def __init__(self):
   ...:         self.a1 = B()
   ...:         

In [2]: class B:
   ...:     def __init__(self):
   ...:         self.b1 = C()
   ...:         

In [3]: class C:
   ...:     def __init__(self):
   ...:         self.c1 = 7
   ...:         

In [4]: from functools import reduce 
In [5]: reduce(getattr, [A(), 'a1', 'b1', 'c1'])
Out[5]: 7

Answer 3

class A:
    def __init__(self, a):
        self.a = a

# create objects with many a  atributes..        
a = A(A(A(A('a'))))


x = a
# as long as a has atribute a continue...
while hasattr(x, 'a'):
    print x
    x = x.a