How to PyArg_ParseTuple the bytearray in Python to C ?

How to PyArg_ParseTuple the bytearray in Python to C?

For example, in Python,

array = bytearray(bytes(random.choice(range(256)) * length))

and sometimes we want to pass this byte array to C using the PyArg_ParseTuple function (Python-C Library).

We can convert the Python bytearray object to a C char* and its length to Py_ssize_t.

Here’s an example to demonstrate this:

#include <Python.h>

static PyObject* my_function(PyObject* self, PyObject* args) {
    Py_buffer view;
    if (!PyArg_ParseTuple(args, "y*", &view)) {
        return NULL;  // Error parsing the argument
    }

    // Now you can access the data using view.buf and view.len
    char* data = (char*) view.buf;
    Py_ssize_t length = view.len;

    // For demonstration, just printing out the first byte
    if (length > 0) {
        printf("First byte: %d\n", (unsigned char)data[0]);
    }

    // Remember to release the buffer when done
    PyBuffer_Release(&view);

    Py_RETURN_NONE;
}

static PyMethodDef MyMethods[] = {
    {"my_function", my_function, METH_VARARGS, "Function to demonstrate bytearray parsing"},
    {NULL, NULL, 0, NULL}  // Sentinel
};

static struct PyModuleDef mymodule = {
    PyModuleDef_HEAD_INIT,
    "mymodule",
    NULL,
    -1,
    MyMethods
};

PyMODINIT_FUNC PyInit_mymodule(void) {
    return PyModule_Create(&mymodule);
}

Here’s a brief explanation:

• We use the “y*” format code in PyArg_ParseTuple to parse the bytearray. This code expects a bytes-like object (including bytes, bytearray, or any object that supports the buffer protocol) and fills a Py_buffer structure.
• The Py_buffer structure provides access to the underlying memory buffer and its metadata (like its length).
• Don’t forget to release the buffer using PyBuffer_Release once you’re done with it to avoid memory leaks.

You can compile this C extension and then use it in Python like this:

import mymodule
import random

length = 10
array = bytearray(bytes(random.choice(range(256)) for _ in range(length)))
mymodule.my_function(array)

When you run the above Python code, it should print out the first byte of the bytearray.

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