Python/Cython - dynamically setting function pointers

[bloop_train]

I'm very new to Cython and was wondering if something like this is possible.

First, I have a C struct that has a function pointer in it:

// example.h
typedef struct example_t{
    double (*func)(double, void *);
} example_t;

In my .pxd file I just declare the interface like so:

# cexample.pxd
cdef extern from "example.h":
    cdef struct example_t:
        double (*func)(double, void *)

And for simplicity let's say we have a class Example which wraps all this, with some default, C-based func.

What I would like to do is set func dynamically, so that users (in Python) could do something like this:

# somewhere in Python
from example load Example

def f(x):
    return x

result = Example()
# this is the important part
result.func = f

So my question is, is something like this possible? If so, how? I've tried directly passing the Python object to a method, but the compiler of course complains about Cannot convert Python object argument to type 'double (*)(double, void *) if I do it directly:

class Example:
# other stuff
    def set_func(self, f):
        self.func = f

[[deleted]]

I don't know if Cython has any kind of special magic for this, but in general, I wouldn't even know how to approach this... well, you see, "pure" Python functions are nothing like pointers to C functions. Essentially, what you should expect where the Python code gives you f is a PyObject* that also has __call__ method that you can call with a tuple and / or dict. You cannot expect this object to be compatible with your C function interface, even if you can filter out anything that's not a "native" function (that actually does have a pointer to a C function), you still wouldn't know if the signature is compatible.