SWIG INOUT types (C++ to Python)

manpreet Best Answer 2 years ago

I'm creating a python wrapper for a C++ api, making support for some types was more or less straightfoward using templates but the api needs some variables by reference, one of them is an int and the other is float.

If I am not wrong it is done by creating a INOUT apply like:

%apply float& INOUT { float& a };
%apply int& INOUT { int& a };

But how I use that types inside my python?

manpreet 2 years ago

These b.com/tag/parameters">parameters are returned from the generated b.com/tag/python">python b.com/tag/function">function (not totally intuitive, considering the wrapped C++ b.com/tag/function">function signature). Let's say this is your exposed b.com/tag/function">function:

%apply float& INOUT { float& a };
%apply int& INOUT { int& b };

void foo(float& a, int& b);

you would invoke it from b.com/tag/python">python as

a = 3.14
b = 42

a, b = foo(a, b)

If you don't capture the return values, a and b remain unchanged.