如何在不破坏默认行为的情况下在Python中重写__getattr__? [英] How do I override __getattr__ in Python without breaking the default behavior?

问题描述

我想重写类上的__getattr__方法以执行一些幻想，但我不想破坏默认行为.

I want to override the __getattr__ method on a class to do something fancy but I don't want to break the default behavior.

正确的方法是什么?

推荐答案

覆盖__getattr__应该没问题-__getattr__仅作为最后的选择，即，如果实例中没有与名称匹配的属性.例如，如果您访问foo.bar，则仅当foo没有名为bar的属性时，才会调用__getattr__.如果该属性是您不想使用的属性，请提高AttributeError:

Overriding __getattr__ should be fine -- __getattr__ is only called as a last resort i.e. if there are no attributes in the instance that match the name. For instance, if you access foo.bar, then __getattr__ will only be called if foo has no attribute called bar. If the attribute is one you don't want to handle, raise AttributeError:

class Foo(object):
    def __getattr__(self, name):
        if some_predicate(name):
            # ...
        else:
            # Default behaviour
            raise AttributeError

但是，与__getattr__不同，__getattribute__将首先被调用(仅适用于新样式类，即从对象继承的样式类).在这种情况下，您可以保留默认行为，如下所示:

However, unlike __getattr__, __getattribute__ will be called first (only works for new style classes i.e. those that inherit from object). In this case, you can preserve default behaviour like so:

class Foo(object):
    def __getattribute__(self, name):
        if some_predicate(name):
            # ...
        else:
            # Default behaviour
            return object.__getattribute__(self, name)

有关更多信息，请参见 Python文档.

See the Python docs for more.

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