How to PyArg_ParseTuple the bytearray in Python to C?
For example, in Python,
1 | array = bytearray(bytes(random.choice(range(256)) * length)) |
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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | #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); } |
#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:
1 2 3 4 5 6 | import mymodule import random length = 10 array = bytearray(bytes(random.choice(range(256)) for _ in range(length))) mymodule.my_function(array) |
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.
–EOF (The Ultimate Computing & Technology Blog) —
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