I am writing a simple Vector implementation as a Python extension module in C that looks mostly like this:
typedef struct {
PyObject_HEAD
double x;
double y;
} Vector;
static PyTypeObject Vector_Type = {
...
};
It is very simple to create instances of Vector while calling from Python, but I need to create a Vector instance in the same extension module. I looked in the documentation but I couldn't find a clear answer. What's the best way to do this?
Simplest is to call the type object you've created, e.g. with PyObject_CallFunction -- don't let the name fool you, it lets you call any callable, not just a function.
If you don't have a reference to your type object conveniently available as a static global to your C module, you can retrieve it in various ways, of course (e.g., from your module object with a PyObject_GetAttrString). But sticking that PyObject* into a static module-level C variable is probably simplest and most convenient.
PyObject_Call... function in the Python C API, it will go through exactly the same steps (and require exactly the same arguments) as when called from Python. The docs I pointed to clearly say Return value: New reference. meaning that you don't need to incref it (understanding new, borrowed and stolen references is crucial to programming to the C Python API, and the docs are always commendably super-explicit about what case applies!-).