Finding a python object in c++

[bmatt]

I am trying to figure out how to get a reference to a python object in
c++ so that I can call methods from c++. For example if I have the
following python code

class foo:
def func():
x = 1

f1 = foo()
f1.func()

How do I find f1 at get a Py_Object* to it so I can call the func
method?

Thanks

 

[jepler]

Access the 'im_self' attribute of the bound function object. In C,
I suppose this is something like
PyObject_GetAttrString(bound_m, 'im_self')
... def m(self): pass
...

f = F()
bound_m = f.m
dir(bound_m) ['__call__', '__class__', '__cmp__', '__delattr__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__repr__', '__setattr__', '__str__', 'im_class', 'im_func', 'im_self']
bound_m.im_self is f

1

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[Brian Matt]

Initially I was confused by your response because of my lack of
knowledge of how the Python interpreter works. I did a bit more
research and things are much more clear. My biggest problem was not
understanding how all defined objects are stored in the dictionary for
the imported module. Once I figured this out I was able to use the
following code to get f1 and call func.

//Assume python initialized and module imported
dict = PyModule_GetDict(module);
PyObject* pInst = PyDict_GetItemString(dict, "f1");
if(pInst) {
PyObject *pValue;
pValue = PyObject_CallMethod(pInst, "func", "");
if(pValue) {
Py_DECREF(pValue);
}
}

Note: this code doesn't handle error situations like making sure the
pInst variable is an instance object

Thanks,
BSMatt

Access the 'im_self' attribute of the bound function object. In C,
I suppose this is something like
PyObject_GetAttrString(bound_m, 'im_self')
... def m(self): pass
...

f = F()
bound_m = f.m
dir(bound_m) ['__call__', '__class__', '__cmp__', '__delattr__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__repr__', '__setattr__', '__str__', 'im_class', 'im_func', 'im_self']
bound_m.im_self is f

1

 

[Alex Martelli]

//Assume python initialized and module imported
dict = PyModule_GetDict(module);
PyObject* pInst = PyDict_GetItemString(dict, "f1");

OK, but needlessly indirect. Doing just:

PyObject* pInst = PyObject_GetAttrString(module, "f1");

should, I think, be preferable.

if(pInst) {
PyObject *pValue;
pValue = PyObject_CallMethod(pInst, "func", "");
if(pValue) {
Py_DECREF(pValue);
}
}

Note: this code doesn't handle error situations like making sure the
pInst variable is an instance object

So much the better! If module.f1 has a func method that is callable
without arguments, why ever would you want to prohibit it from being
whatever type it wants to be? Maybe one day you'll want to recode the
whole type in C, and if you'd gone to the misplaced trouble of "making
sure [it] is an instance object" you'd just be creating headaches for
yourself...


Alex