What Does PyCapsule_New Do?

What Does PyCapsule_New Do? 🔗

Imagine you’ve got a precious nugget of data—perhaps a C pointer—that you want to safely pass around while ensuring it stays intact. PyCapsule_New is your treasure chest. It lets you wrap this nugget in a Python object, providing a safe, magical box that can be passed around, keeping its contents secure and unaltered.

How PyCapsule_New is Used 🔗

Using PyCapsule_New is fairly straightforward. Its primary role is to create a new capsule object containing a pointer to your data, a name for identification, and optional destructor functions. Here’s a basic example to get you started:

#include <Python.h>

int my_data = 42; // This is your precious C data

// Destructor function to clean up when capsule is deleted
void my_destructor(PyObject *capsule) {
    int *ptr = (int *)PyCapsule_GetPointer(capsule, "my_data");
    // Perform necessary cleanup
    printf("Cleaning up: %d\n", *ptr);
}

// Create a new capsule
PyObject *capsule = PyCapsule_New(&my_data, "my_data", my_destructor);
if (!capsule) {
    // Handle error
    return NULL;
}

// To retrieve the wrapped pointer:
int *retrieved_ptr = (int *)PyCapsule_GetPointer(capsule, "my_data");
printf("Retrieved data: %d\n", *retrieved_ptr);

In this example:

1. my_data: Our golden nugget (an integer) that we want to store safely.
2. my_destructor: A function to clean up when the capsule is no longer needed.
3. PyCapsule_New: Creates a new capsule containing my_data, identified by “my_data”, with my_destructor as the cleanup function.

How PyCapsule_New Works 🔗

Think of capsules as data containers that keep your C pointers (“nuggets”) safe inside, away from prying eyes and meddling hands. Here’s a closer look under the hood:

1. Creation: PyCapsule_New takes your C data pointer, an optional name, and an optional destructor. It wraps these in a Python object that behaves like a capsule.

2. Naming: Assigning a name to your capsule is like putting a label on your box. When retrieving the pointer, it ensures you’re opening the right container.

3. Destruction: The destructor function acts like a responsible janitor, cleaning up resources when the capsule is no longer in use. No need to worry about memory leaks or lingering data.

4. Retrieval: PyCapsule_GetPointer helps you fetch the stored pointer when you need it—just ensure the name matches the label on your box.

A pro tip: Always ensure your names match when creating and retrieving capsules. Think of it as using the right key for the right lock.