我怎么能从字典中称呼__missing__ [英] How can I call __missing__ from dict

问题描述

我想从dict派生并覆盖缺少的方法.我想做一些事情，然后仍然调用它的超级功能.像这样:

I would like to derive from dict and overwrite the method missing. I would like to do some stuff and then still call its super function. Something like this:

class Foo(dict):
    def __missing__(self, key):
        print('missing {}'.format(key))
        return super().__missing__(key)

但是会产生:

AttributeError: 'super' object has no attribute '__missing__'

当然我仍然可以使用以下方法制作一个工作程序:

Of course I could still make a working program using:

raise KeyError(key)

但是我更愿意称其为超级功能.因为代码可以(或者可能会在未来的python版本中)在super().__missing__中执行，而不是引发KeyError.

But I would much rather call the super function. Because code could (or maybe at a future version of python will be) executed in super().__missing__ other than raising the KeyError.

推荐答案

没有dict.__missing__；只需将呼叫放到super().__missing__(并调出KeyError).该方法是可选，并且没有默认实现.

There is no dict.__missing__; just drop the call to super().__missing__ (and raise a KeyError). The method is optional and has no default implementation.

或者，如果您想正确地支持多重继承，则可以捕获AttributeError异常:

Alternatively, if you want to support multiple inheritance properly, you could catch the AttributeError exception:

class Foo(dict):
    def __missing__(self, key):
        print('missing {}'.format(key))
        try:
            return super().__missing__(key)
        except AttributeError:
            raise KeyError(key)

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