CODEWITHSUNDEEP
pythonc++cswigctypes
Totte Karlsson
Totte Karlsson

Reputation: 1341

How to cast a SwigPyObject to ctypes void*

I have a python, ctypes wrapped function to a C API taking a void* parameter for a class X, e.g. C: 

myFunc(void* aXHandle); //where X is a class, of class X.

For the class X, I have access to a swigged API and can get the myX.this, which is of type SwigPyObject.

How do I cast this so I can call my C-API function using ctypes and using a ctypes c_void_p as an argument? In Python, I thought something like: aXObjectThis = myX.this

myHandle = cast(aXObjectThis, c_void_p)

but that does not work; getting "wrong type in argument 1"

Upvotes: 1

Views: 1715

Answers (1)

Eryk Sun
Eryk Sun

Reputation: 34260

The __int__ method of SwigPyObject is handled by SwigPyObject_long, defined in pyrun.swg. It returns PyLong_FromVoidPtr(v->ptr), so you should be able to use the following:

myHandle = c_void_p(int(myX.this))

More conveniently ctypes looks for an _as_parameter_ attribute. You could set this on the instance or as a property:

type(myX)._as_parameter_ = property(
    lambda self: c_void_p(int(self.this)))

The simply call myFunc(myX).

Upvotes: 3

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