Python：为什么__getattr__捕获AttributeErrors？ [英] Python: Why is __getattr__ catching AttributeErrors?

问题描述

我正在努力使用 __ getattr __ 。我有一个复杂的递归代码库，重要的是让异常传播。

I'm struggling with __getattr__. I have a complex recursive codebase, where it is important to let exceptions propagate.

class A(object):
    @property
    def a(self):
        raise AttributeError('lala')

    def __getattr__(self, name):     
        print('attr: ', name)
        return 1      

print(A().a)

结果：

('attr: ', 'a')
1

为什么会这样的行为？为什么没有抛出异常？没有记录此行为（ __ getattr __ 文档）。 getattr（）只能使用 A .__ dict __ 。任何想法？

Why this behaviour? Why is no exception thrown? This behaviour is not documented (__getattr__ documentation). getattr() could just use A.__dict__. Any thoughts?

推荐答案

我只是将代码更改为

class A(object):
    @property
    def a(self):
        print "trying property..."
        raise AttributeError('lala')
    def __getattr__(self, name):     
        print('attr: ', name)
        return 1      

print(A().a)

，我们看到，确实首先尝试该属性。但是，由于它声称不在那里（通过提高 AttributeError ）， __ getattr __（）被称为最后手段

and, as we see, indeed the property is tried first. But as it claims not to be there (by raising AttributeError), __getattr__() is called as "last resort".

没有清楚的记录，但是可能会被计入在通常的地方没有找到属性查找时调用。

It is not documented clearly, but can maybe be counted under "Called when an attribute lookup has not found the attribute in the usual places".

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