[FIXED] PyQt: How to send parameters by reference with QAxWidget

Issue

I'm attempting to use PyQt to talk to an ActiveX COM object in Python. This method works in Python:

myobj.dynamicCall('SetAbsMovePos(int, double)', [0, 10])

However, I can't send arguments by reference. From the docs, the method I wish to call is:

int GetNumHWUnits (int lHWType, int& plNumUnits)

and the basic example code is:

QVariantList params = ...
int result = object->dynamicCall("GetNumHWUnits(int, int&)", params).toInt();

I presume the equivalent code in Python, using ctypes, should be:

num = ctypes.c_int()
myobj.dynamicCall('GetNumHWUnits(int, int&)', [6, ctypes.byref(num)])

but num is never updated.

What's the equivalent code or workaround in Python, and how can I send and later read an argument of type int& using Python?

Solution

Got the solution from the PyQt mailing list. A reference to the list of arguments is needed, as only that list is updated; the original QVariant objects never are. Seems fairly obvious in retrospect!

typ = QVariant(6)
num = QVariant(0)
args_list = [typ, num]

self.dynamicCall('GetNumHWUnits(int, int&)', args_list)

print 'Num of HW units =', args_list[1].toInt()[0]

A full code example is shown in this post.

Answered By - 101