PyArg_ParseTuple and a callback function pointer

Question

I have code like the following:

    PyObject *callback;
    PyObject *paths;

    // Process and convert arguments
    if (!PyArg_ParseTuple(args, "OO:schedule", &paths, &callback))
            return NULL;

What exactly happens inside PyArg_ParseTuple? My guess is that callback gets the function pointer I passed to args (also PyObject*). How does PyArg_ParseTuple convert the function pointer to PyObject*?

What I want to know is what happens if I pass in the same callback function pointer twice. I think callback gets allocated a new PyObject inside PyArg_ParseTuple, so it will get a different memory address each time, but will contain the same callback function pointer.

But if I PyObject_Hash callback, it will produce a different value each time, right? (since address is different each time..)

John Machin · Accepted Answer · 2010-08-22 12:00:56Z

1

PyArg_ParseTuple doesn't care about the type of an "O" arg. No conversion is done. No new object is created. The address of the object is dropped into the PyObject * C variable that you have specified. It does exactly the same to each of your two args.

I can't imagine what is the relevance of PyObject_Hash. If you want to compare two incarnations of your callback arg, just use == on the addresses.

answered Aug 22, 2010 at 12:00

John Machin

83.2k12 gold badges147 silver badges193 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Xavier Combelle · Accepted Answer · 2010-08-22 10:59:40Z

0

The point is that if you pass the same callback twice it will receive two objects but you will never be allowed to read only one which is the las wrote. You will have a kind of memory leak as one of the two pointers will not be referenced. Of course the garbage collector will eventually pass after you to clean all the mess. But anyhow...

I misread the PyObject_Hash should be called on callback and paths. It will be the same. but you probably want to compare callback and paths: if(callback==paths) {printf("it 's the same callabck");}

edited Aug 22, 2010 at 10:59

answered Aug 20, 2010 at 17:14

Xavier Combelle

11.3k5 gold badges30 silver badges53 bronze badges

1 Comment

Paul Over a year ago

What I want is to be able to know that it's the same callback function. How do I do that?

Collectives™ on Stack Overflow

PyArg_ParseTuple and a callback function pointer

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related