实现functools.partial，它附加了其他参数 [英] implementing functools.partial that prepends additional arguments

问题描述

functools.partial 的文档说它大致相当于":

The documentation for functools.partial says that it is "roughly equivalent to":

def partial(func, *args, **keywords):
    def newfunc(*fargs, **fkeywords):
        newkeywords = keywords.copy()
        newkeywords.update(fkeywords)
        return func(*(args + fargs), **newkeywords)  # line to change
    newfunc.func = func
    newfunc.args = args
    newfunc.keywords = keywords
    return newfunc

如果我想实现一个附加附加参数的版本， 看来我只需要更改指示的行即可.

If I wanted to implement a version that prepends the additional arguments, it seems like I'd just have to change the indicated line.

仅复制此代码，我是否还要担心其他功能/陷阱?

Are there any other features/gotchas that I should be worried about in just copying this code?

推荐答案

查看 _functoolsmodule.c ，我认为没有什么可担心的.

Looking at the source code for _functoolsmodule.c, I don't think there's much to worry about.

partial的模块实现处理酸洗和repr，但是其他所有功能都像在文档中一样工作，因此大概在C中实现它的原因只是为了提高效率.还有一个事实，它是类型，而不仅仅是函数闭包.

The module implementation of partial handles pickling and repr, but everything else looks like it works as in the documentation so presumably the reason it is implemented in C is just for efficiency. There is also the fact that it is a type rather than just being a function closure.

但是，请注意，在文档示例func，args和keywords中，这些纯属修饰；也就是说，它们不能像实际的functools.partial实例那样被覆盖.一种替代方法是子类functools.partial:

Note, however, that in the documentation example func, args, and keywords are purely cosmetic; i.e. they are not overridable as they are with actual functools.partial instances. One alternative would be to subclass functools.partial:

class rpartial(partial):
    def __call__(self, *args, **kwargs):
        kw = self.keywords.copy()
        kw.update(kwargs)
        return self.func(*(args + self.args), **kw)

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