问题
How to parse userdefined types (or types from an existing non-standard library) using PyArg_ParseTuple?
回答1:
Instead of using the plain O format, as Martijn suggested, I normally prefer using the O& format. It allows you to pass a function that will be called to convert any PyObject* to an arbitrary C (double) pointer. Here is some example usage, in which I'm converting a passed value to a pointer to my own object type:
/**
* This method should return 0 if it does not work or 1 in case it does
* PyArg_*() functions will handle the rest from there or let your program
* continue in case things are fine.
*/
int MyConverter(PyObject* o, MyOwnType** mine) {
//write the converter here.
}
Then, at the point you need to parse your object:
/**
* Simple example
*/
static PyObject* py_do_something(PyObject*, PyObject* args, PyObject* kwds) {
/* Parses input arguments in a single shot */
static char* kwlist[] = {"o", 0};
MyOwnType* obj = 0; ///< if things go OK, obj will be there after the next call
if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&", kwlist, &MyConverter, &obj))
return 0; ///< we have failed, let Python check exceptions.
/* if you get to this point, your converter worked, just use */
/* your newly allocated object and free it, when done. */
}
The advantage of this approach is that you can encapsulate your MyConverter on a C-API and then re-use it in other functions for the the same job.
回答2:
Custom python classes can be parsed using the O format:
O(object) [PyObject *]
Store a Python object (without any conversion) in a C object pointer. The C program thus receives the actual object that was passed. The object’s reference count is not increased. The pointer stored is not NULL.
来源：https://stackoverflow.com/questions/19282054/parsing-user-defined-types-using-pyarg-parsetuple