Python C API sys.getsizeof()

Question

I’m trying to call a method getsizeof from a C library for Python.
Here’s my code:

//Returns in bytes the size of obj in memory
//sys.getsizeof(obj)
size_t getSizeOf(PyObject* obj){ //obj could be dict or list
    Py_INCREF(obj);

    PyObject* sys = PyModule_New("sys"); //import sys

    PyObject* string = Py_BuildValue("s", "getsizeof");

    PyObject* res = PyObject_CallMethodObjArgs(sys, string, obj, NULL); //res = sys.getsizeof(obj)
    Py_DECREF(sys);
    Py_DECREF(string);

    long tmp = PyLong_AsLong(res);
    Py_DECREF(res);

    Py_DECREF(obj);
    return (size_t)tmp;
}

And this code gives me a segfault. No clue why. What am I doing wrong?

Asked By: TCA 166

||

Source

Answer 1

Use PyImport_ImportModule to import a module. Also using PyObject_CallMethod simplifies the call. Incrementing the incoming obj is not needed.

#include <Python.h>

__declspec(dllexport)  // For Windows
size_t getSizeOf(PyObject* obj) {
    PyObject* sys = PyImport_ImportModule("sys");
    PyObject* res = PyObject_CallMethod(sys, "getsizeof", "O", obj);
    Py_DECREF(sys);
    long tmp = PyLong_AsLong(res);
    Py_DECREF(res);
    return (size_t)tmp;
}

Calling method from Python:

>>> import ctypes as ct
>>> dll = ct.PyDLL('./test')
>>> x=[1,2,3]
>>> dll.getSizeOf.argtypes = ct.py_object,
>>> dll.getSizeOf.restype = ct.c_size_t
>>> dll.getSizeOf(x)
88
>>> import sys
>>> sys.getsizeof(x) # to verify
88

Answered By: Mark Tolonen

Python C API sys.getsizeof()

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