Python C扩展-为什么将使用关键字参数的方法强制转换为PyCFunction [英] Python C Extension - Why are methods that use keyword arguments cast to PyCFunction

问题描述

我正在学习Python-C扩展，并对为什么必须将使用关键字参数的方法强制转换为PyCFunctions感到困惑.

I've am learning about Python-C extensions and am puzzled as to why methods that use keyword arguments must be cast to PyCFunctions.

我对PyCFunction的理解是，它需要两个指向PyObject的指针，并返回一个指向PyObject的指针-例如.

My understanding of a PyCFunction is that it takes two pointers to PyObjects and returns a single pointer to a PyObject - e.g.

 PyObject* myFunc(PyObject* self, PyObject* args)

如果我要使用使用关键字参数的函数，则此函数将使用三个指向PyObject的指针，并返回指向PyObject的单个指针-例如.

If I'm going to use a function that uses keyword arguments, then this function will take three pointers to PyObjects and returns a single pointer to a PyObject - e.g.

 PyObject* myFunc(PyObject* self, PyObject* args, PyObject* keywordArgs)

但是，当我创建模块函数数组(用于名为"adder"的函数)时:

However, when I create the module functions array (for a function called 'adder'):

{ "adder", (PyCFunction)adder, METH_VARARGS | METH_KEYWORDS, "adder method" }

正常工作.感觉就像我将一个float转换为一个int并仍然必须使用float的非整数部分一样.如果我没有看到这项工作，我会以为那是行不通的.我在这里不明白什么?

works fine. It feels like I cast a float to an int and still got to use the non-integer parts of the float. If I didn't see this work, I would have thought it wouldn't work. What am I not understanding here?

此外，我看到了一些对PyCFunctionWithKeywords的引用，这些引用似乎具有我认为我需要的功能签名，但是我的编译器抱怨(发出警告)不兼容的指针类型".

Also, I saw some references to a PyCFunctionWithKeywords, which seems to have the function signature I thought I needed, but my compiler complained (gave warnings) about 'incompatible pointer types'.

不赞成使用PyCFunctionWithKeywords吗?如果没有，我是否应该/必须使用它?

Was PyCFunctionWithKeywords deprecated? If not, is there a time when I should/must use it?

推荐答案

如果您的函数处理关键字参数，则它必须对应于PyCFunctionWithKeywords.但是，C并不会进行重载，并且PyMethodDef构建的结构被定义为具有PyCFunction，而不是完全未经检查的void *.因此，您必须将PyCFunctionWithKeywords强制转换为PyCFunction才能阻止编译器抱怨.

If your function handles keyword arguments, then it must correspond to a PyCFunctionWithKeywords. However, C doesn’t do overloading, and the structure built by PyMethodDef is defined to expect a PyCFunction, rather than, say, a completely unchecked void *. So you must cast your PyCFunctionWithKeywords to a PyCFunction to stop the compiler complaining, that’s all.

请记住，您还必须在标志中传递METH_KEYWORDS，以告诉Python您的函数具有PyCFunctionWithKeywords的签名，而不是PyCFunction的签名.

Remember that you must also pass METH_KEYWORDS in the flags to tell Python that your function has the signature of a PyCFunctionWithKeywords, not a PyCFunction.

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