python - 属性错误 : undesired interaction between @property and __getattr__

Question

我在 @property 中结合 python 中的 __getattr__() 引发了 AttributeErrors 的问题:

示例代码:

>>> def deeply_nested_factory_fn():
...     a = 2
...     return a.invalid_attr
...
>>> class Test(object):
...     def __getattr__(self, name):
...         if name == 'abc':
...             return 'abc'
...         raise AttributeError("'Test' object has no attribute '%s'" % name)
...     @property
...     def my_prop(self):
...         return deeply_nested_factory_fn()
...
>>> test = Test()
>>> test.my_prop
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in __getattr__
AttributeError: 'Test' object has no attribute 'my_prop'

在我的例子中，这是一个极具误导性的错误消息，因为它隐藏了 deeply_nested_factory_fn() 有错误的事实。

---

根据 Tadhg McDonald-Jensen 的回答中的想法，我目前最好的解决方案如下。任何关于如何去掉 AttributeError 的 __main__. 前缀以及回溯中对 attributeErrorCatcher 的引用的任何提示都将不胜感激。

>>> def catchAttributeErrors(func):
...     AttributeError_org = AttributeError
...     def attributeErrorCatcher(*args, **kwargs):
...         try:
...             return func(*args, **kwargs)
...         except AttributeError_org as e:
...             import sys
...             class AttributeError(Exception):
...                 pass
...             etype, value, tb = sys.exc_info()
...             raise AttributeError(e).with_traceback(tb.tb_next) from None
...     return attributeErrorCatcher
...
>>> def deeply_nested_factory_fn():
...     a = 2
...     return a.invalid_attr
...
>>> class Test(object):
...     def __getattr__(self, name):
...         if name == 'abc':
...             # computing come other attributes
...             return 'abc'
...         raise AttributeError("'Test' object has no attribute '%s'" % name)
...     @property
...     @catchAttributeErrors
...     def my_prop(self):
...         return deeply_nested_factory_fn()
...
>>> class Test1(object):
...     def __init__(self):
...         test = Test()
...         test.my_prop
...
>>> test1 = Test1()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __init__
  File "<stdin>", line 11, in attributeErrorCatcher
  File "<stdin>", line 10, in my_prop
  File "<stdin>", line 3, in deeply_nested_factory_fn
__main__.AttributeError: 'int' object has no attribute 'invalid_attr'

Answer 1

如果你愿意专门使用新式类，你可以重载 __getattribute__ 而不是 __getattr__:

class Test(object):
    def __getattribute__(self, name):
        if name == 'abc':
            return 'abc'
        else:
            return object.__getattribute__(self, name)
    @property
    def my_prop(self):
        return deeply_nested_factory_fn()

现在您的堆栈跟踪将正确提及 deeply_nested_factory_fn。

Traceback (most recent call last):
  File "C:\python\myprogram.py", line 16, in <module>
    test.my_prop
  File "C:\python\myprogram.py", line 10, in __getattribute__
    return object.__getattribute__(self, name)
  File "C:\python\myprogram.py", line 13, in my_prop
    return deeply_nested_factory_fn()
  File "C:\python\myprogram.py", line 3, in deeply_nested_factory_fn
    return a.invalid_attr
AttributeError: 'int' object has no attribute 'invalid_attr'