是否可以将自己的装饰器应用于Python中的内置方法？ [英] Is it possible to apply my own decorators to builtin methods in Python?

问题描述

我刚遇到Python装饰器。只是出于兴趣，您能以某种方式将自己的装饰器应用于内置对象方法吗？说我想应用这个：

I've just come across Python decorators. Just out of interest, can you apply your own decorator to a built-in object method somehow? Say I wanted to apply this:

def remove_empty(fn):
    def filtered():
        return filter(lambda x: x != '', fn())
    return filtered

为此：

some_string.split('\n')

以便删除空字符串。可能吗？甚至是个好主意？

in order to remove empty strings. Is it possible? Or even a good idea?

推荐答案

从某种意义上讲是可能的；这取决于您的意思。这样的装饰器语法...

It's possible in a sense; it depends on what exactly you mean. Decorator syntax like this...

@dec
def foo():
    pass

实际上只是糖：

def foo():
    pass
foo = dec(foo)

因此，没有什么可以阻止您在全局名称空间的预定义函数上使用装饰器。

So there's nothing to stop you from using a decorator on a predefined function in the global namespace.

func = dec(func)

但是内置类的方法位于该类的名称空间中，并且不能直接修改该名称空间，例如 chepner 已经指出。这是一件好事，因为它可以确保 str 类型的对象能够按预期运行！但是，您可以 subclass str并以这种方式装饰该方法。 （以下内容在Python 2中有效；在Python 3中，将 filter 的输出传递给列表。 super 也可能工作方式略有不同；我以后会发布Python 3更新。）

But the methods of built-in classes live in the namespace of that class, and that namespace can't be modified directly, as chepner has already pointed out. That's a good thing, because it ensures that objects of type str will behave as expected! However, you could subclass str and decorate the method that way. (The below works in Python 2; in Python 3, pass the output of filter to a list. super also may work a little differently; I'll post a Python 3 update in the future.)

>>> def remove_empty(fn):
...     def filtered(*args, **kwargs):
...         return filter(lambda x: x != '', fn(*args, **kwargs))
...     return filtered
... 
>>> class WeirdString(str):
...     @remove_empty
...     def split(self, *args, **kwargs):
...         return super(WeirdString, self).split(*args, **kwargs)
... 
>>> 'This decorator is unnecessary\n\n\n'.split('\n')
['This decorator is unnecessary', '', '', '']
>>> WeirdString('This decorator is unnecessary\n\n\n').split('\n')
['This decorator is unnecessary']

或更直接（以及更多使用装饰器的精神）：

Or more directly (and so more in the spirit of decorator use):

>>> class WeirdString2(str):
...     split = remove_empty(str.split)
... 
>>> WeirdString2('This decorator is unnecessary\n\n\n').split('\n')
['This decorator is unnecessary']

在此特殊示例中，我希望使用显式过滤器。但是我可以想象，例如，一个内置类的子类，它执行一些记忆力之类的东西。

In the case of this particular example, I'd prefer an explicit filter. But I can imagine, for example, a subclass of a built-in class that does some memoization or something like that.

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