object: always return the same value for Py_None, Py_True, and Py_False

[icholy]

https://docs.python.org/2/c-api/none.html

You're supposed to be able to compare a python.PyObject to python.Py_None but this doesn't work.

I think we should consider adding a PyNone_Check function to compare the underlying pointer.

// Return true if self is None
func PyNone_Check(self *PyObject) bool {
	return Py_None.ptr == self.ptr
}

[sbinet]

alternatively, and to make it behave more like the C API, one could modify togo to check the ptr pointer for C.Py_None and return python.Py_None.
https://github.com/sbinet/go-python/blob/master/object.go#L36

WDYT?

[icholy]

That's a way better solution.

[icholy]

We should probably do the same with Py_True and Py_False

[sbinet]

SGTM.

[icholy]

There's an initialisation loop:

var Py_None = togo(C._gopy_pynone())

func togo(obj *C.PyObject) *PyObject {
	switch obj {
	case nil:
		return nil
	case Py_None.ptr:
		return Py_None
	case Py_True.ptr:
		return Py_True
	case Py_False.ptr:
		return Py_False
	default:
		return &PyObject{ptr: obj}
	}
}

# github.com/sbinet/go-python
./none.go:9:5: initialization loop:
	/home/icholy/go/src/github.com/sbinet/go-python/none.go:9:5 Py_None refers to
	/home/icholy/go/src/github.com/sbinet/go-python/object.go:36:6 togo refers to
	/home/icholy/go/src/github.com/sbinet/go-python/none.go:9:5 Py_None

We can either not use the togo function for initialising Py_None, Py_True, and Py_False.

var Py_None = &Object{C._gopy_pynone()}
// etc ...

or split togo into two functions.

func togo(obj *C.PyObject) *PyObject {
	switch obj {
	case Py_None.ptr:
		return Py_None
	case Py_True.ptr:
		return Py_True
	case Py_False.ptr:
		return Py_False
	default:
		return newgo(obj)
	}
}

func newgo(obj *C.PyObject) *PyObject {
	if obj == nil {
		return nil
	}
	return &PyObject{ptr: obj}
}

var Py_None = newgo(C._gopy_pynone())

what do you think?

[icholy]

I went with the 2 functions

[sbinet]

I must say I am unsure about the approach of these 2 very similarly-looking functions that do almost the same thing but not quite.

I think it would be as simple to leave only one function (togo) and initialize the 3 global variables like so:

var Py_None = &PyObject{ptr: C._gopy_none()}
var Py_False = &PyObject{ptr: C._gopy_pyfalse()}
var Py_True = &PyObject{ptr: C._gopy_pytrue()}

[icholy]

no problem

[icholy]

@sbinet should be good to go