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__str __ () is not called when printing a C ++ class wrapped for Python using SWIG

I am trying to print the C ++ classes that I wrapped for Python using SWIG. I followed the documentation and this question: How is a stringfy swig matrix object in python

There is an extended function __str__, but it is not called when I print an object from Python. Let me give a minimal example:

TestClass.h

#include <iostream> 

class TestClass{
private:
    int my_int;
public:
    TestClass():
        my_int(0)
    {}

    friend std::ostream& operator<< (std::ostream& o, TestClass const& t){
        o<< "TestClass: " << t.my_int;
        return o;
    }
};

Testclass.cpp

#include "TestClass.h"

int main(){
    using namespace std;
    TestClass t;
    cout << t << endl;
}

TestClass.i

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

const char* __unicode__() { 
  std::cout << "unicode: " << *$self << std::endl;
  std::ostringstream out; 
  out << *$self; \
  return out.str().c_str(); 
}
%enddef

%extend TestClass{
    __STR__()
};

CMakeLists.txt

cmake_minimum_required (VERSION 2.6)
project (battery_lib_cpp)
set(CMAKE_VERBOSE_MAKEFILE 1)

FIND_PACKAGE(SWIG REQUIRED)
INCLUDE(${SWIG_USE_FILE})
SET(CMAKE_SWIG_FLAGS "-Wall")

#look for Pythonlibs
FIND_PACKAGE(PythonLibs)
INCLUDE_DIRECTORIES(${PYTHON_INCLUDE_PATH})
INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})

SET_SOURCE_FILES_PROPERTIES(TestClass.i PROPERTIES CPLUSPLUS ON)
SET_PROPERTY(SOURCE TestClass.i PROPERTY SWIG_FLAGS "-builtin")

SWIG_ADD_MODULE(TestClass python TestClass.i TestClass.cpp)

After creating (cmake., Make), I get the following:

matthias@rp3deb:~/dvl/swig_str_minimal$ python
Python 2.7.8 (default, Jul 26 2014, 15:25:14) 
[GCC 4.9.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import TestClass
>>> t = TestClass.TestClass()
>>> print t
<Swig Object of type 'TestClass *' at 0x7f1dffcb2b90>
>>> print t.__str__()
TestClass: 0
TestClass: 0
>>> print t.__str__
<built-in method __str__ of TestClass object at 0x7f1dffcb2b90>

Another test for __unicode__()

>>> import TestClass
>>> t = TestClass.TestClass()
>>> print str(t)
<Swig Object of type 'TestClass *' at 0x7f6584ae4b58>
>>> print t
<Swig Object of type 'TestClass *' at 0x7f6584ae4b58>
>>> print t.__unicode__()
unicode: TestClass: 0
TestClass: 0
>>> print t.__unicode__
<built-in method __unicode__ of TestClass object at 0x7f6584ae4b58>

The expected result should be to __str__()invoke "print t" implicitly. What am I missing?

+4
source share
2

str(x), ++ SWIG, swig -python -builtin, . %feature("python:slot", ...) SWIG, :

%module test

%include <std_string.i>

%feature("python:slot", "tp_str", functype="reprfunc") foo::as_string;

%inline %{
struct foo {
  std::string as_string() const { return "Hello world"; }
};
%}

SWIG 2.0 Python 2.7 :

import test

print str(test.foo())
print repr(test.foo())

:

Hello world
<Swig Object of type 'foo *' at 0xb727ac40>

- , -builtin .

SWIG 2.0.

+3

Flexo, , ( cmake ).

TestClass.i

%module TestClass

%{
#include <sstream>
#include "TestClass.h"
%}
%include "TestClass.h"

//http://stackoverflow.com/questions/2548779/how-to-stringfy-a-swig-matrix-object-in-python
%define __STR__(class_name) 
%feature("python:slot", "tp_str", functype="reprfunc") class_name::py_to_string();

%extend class_name{
    const char* py_to_string() { 
      std::ostringstream out; 
      out << *$self; 
      return out.str().c_str(); 
    }
}
%enddef

__STR__(TestClass);

:

matthias@rp3deb:~/dvl/swig_str_minimal$ python -c "import TestClass; print TestClass.TestClass()"
TestClass: 0
0

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