How to stringfy a swig matrix object in python

Question

I am using swig wrapper of openbabel (written in C++, and supply a python wrapper through swig)

Below i just use it to read a molecule structure file and get the unit

Answer 1

Further to the answer from @jhoon, it seems that SWIG doesn't recognise the std::string return type so change the function to return const char*. Also, since it is a function outside the class, you can't use self but you must use SWIG's $self variable.

So, in the SWIG .i file, if you put the following:

%extend OpenBabel::matrix3x3 {
  const char* __str__() {
    std::ostringstream out;
    out << *$self;
    return out.str().c_str();
  }
};

you should get the desired result when calling Python's print on a matrix3x3.

If you find yourself adding this to many classes, consider wrapping it in a macro like:

%define __STR__()
const char* __str__() {
  std::ostringstream out;
  out << *$self;
  return out.str().c_str();
}
%enddef

and then adding it to the class with:

%extend OpenBabel::matrix3x3 {
  __STR__()
};