CODEWITHSUNDEEP
python
Gio
Gio

Reputation: 3340

How to make a Python C function call to multiply 2 floats?

I'm practicing with making C function calls from python (2.7).

I've succeed the example which is outlined on https://docs.python.org/2/extending/extending.html

Now I'm adjusting this example to multiply 2 floats and return the result. I've implemented the following function in my c source file.

static PyObject *demo_multiply(PyObject *self, PyObject *args)
{
    const float *command;
    float x;

    if (!PyArg_ParseTuple(args, "f", &command)) return NULL;
    x = command[0] * command[1];
    return Py_BuildValue("f", x);
}

And I'm calling this function in python as follows:

print(demo.multiply((2.0, 4.0))

Which results in the following output:

Traceback (most recent call last): File "main.py", line 12, in print(demo.multiply((2.0, 4.0))) TypeError: a float is required

Clearly there is some mistake in my implementation, however I can't figure out what it is as believe I've quite clearly followed documentation on docs.python.org. Can somebody please point out what I'm missing here?

Upvotes: 4

Views: 144

Answers (1)

Gio
Gio

Reputation: 3340

Thanks to user user2357112 comments, I've solved the problem. I've posted the code here for people encountering a similar problem.

(C)

static PyObject *demo_multiply(PyObject *self, PyObject *args)
{
    float y[2];
    float x;

    if (!PyArg_ParseTuple(args, "ff", &(y[0]), &(y[1]))) return NULL;
    x = y[0] * y[1];
    return Py_BuildValue("f", x);
}

(Python)

print(demo.multiply(2.0, 4.0))

Upvotes: 4

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