repr function in swig for python

Question

I have a Swig wrapper to use in python. For one of my class, I have created a repr function as follows

%module myModule
%{
    #include <string>
    #include <sstream>
%}

%extend myClass {
std::string __repr__()
{
    std::ostringstream ss;
    ss << "MyClass(attr1=" << $self->attr1 << ", attr2=" << $self->attr1 << ")";

    return ss.str();
}}

However when I compile the wrapper and use it in python, I get the following error __repr__ returned non-string (type SwigPyObject)

How can I fix this?

Answer 1

Here's a working example of my comment in the question in a self-contained SWIG interface file. As mentioned you need to include SWIG's std_string.i support interface:

example.i

%module example

%{
#include <string>
#include <sstream>
%}

%include <std_string.i>

// Filling in missing minimal class definition.
%inline %{
class myClass {
public:
    int attr1;
    int attr2;
    myClass(int a1, int a2) : attr1(a1), attr2(a2) {}
};
%}

%extend myClass {
std::string __repr__()
{
    std::ostringstream ss;
    ss << "MyClass(attr1=" << $self->attr1 << ", attr2=" << $self->attr1 << ")";

    return ss.str();
}
}

Demo:

>>> import example as e
>>> m = e.myClass(5,7)
>>> m
MyClass(attr1=5, attr2=5)