[capi-sig] Getting Numbers in C

Campbell Barton cbarton at metavr.com
Wed Jul 11 12:58:19 CEST 2007

Iv noticed that theres no one liner way to get a number (double) from a 
PyNumber from the C api.

PyFloat_AsDouble - http://www.python.org/doc/api/floatObjects.html
- Does what I want, but only works on PyFloat (and PyInts), not user 
implementations of the PyNumber protocol.

PyNumber_Float - http://www.python.org/doc/api/number.html
- does what I need but, returnd a PyFloat that needs to then be passed 
to PyFloat_AsDouble,

Id like somthing like PyNumber_AsDouble,

thinking of writing a utility function for this that could read...

/* assumes PyNumber_Check has been tested, should not segfault either way */
double PyNumber_AsDouble(PyObject * value)
	if (PyFloat_Check(value) || PyInt_Check(value)) {
		return PyFloat_AsDouble(value);
	} else {
		PyObject *pyfloat;
		double d;

		pyfloat = PyNumber_Float(value);
		d = PyNumber_AsDouble(pyfloat);
		return d;

Using PyNumber_Float for all values would be a bit slower since it needs 
to make a new pyfloat each time which is why Id prefer to use 
PyFloat_AsDouble where possible.

Wondering if other people would fine something like this useful in the 
Py/C api - or if Im missing something.


Campbell J Barton (ideasman42)

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