CODEWITHSUNDEEP
pythonc++templatesswig
Endou Mamoru
Endou Mamoru

Reputation: 43

Python Error:No constructor defined in SWIG generated module of C++ templated code

I'm trying to make a generic stack in C++ and then trying to build a module of it and extend it to Python using SWIG.
For that, code in templated_stack.h is as follows

#include <string>
template <typename T>
class mNode {
public:
    T data;
    mNode* next;
    /* mNode() { } */
    mNode(T d) { 
        data = d;
        next = NULL;
    }

};
template <typename T>
class mStack {
    mNode<T> *topOfStack;
    mStack();   
    void push(T data);
    T pop();
};

template <class T> mStack<T>::mStack() {
    topOfStack = NULL;
}

template <class T> void mStack<T>::push(T data) {
    mNode<T>* newNode = new mNode<T>(data);
    newNode->next = topOfStack;
    topOfStack = newNode;
}

template <class T> T mStack<T>::pop(void) {
    mNode<T>* tempTop = topOfStack;
    T dataToBePopped = tempTop->data;
    topOfStack = topOfStack->next;
    delete tempTop;
    return dataToBePopped;
}

The interface file I've written is templated_stack.i as follows

%module TemplatedStack
%{
        #include <string>
        #include "templated_stack.h"
%}

%include "templated_stack.h"

%template(IntStack) mStack <int>;

And I'm compiling and building module by following script compileScript.sh which has following code

swig -c++ -python -o templated_stack_wrap.cpp templated_stack.i
g++ -c -fPIC templated_stack_wrap.cpp -I/usr/include/python2.7
g++ -shared -o _TemplatedStack.so templated_stack_wrap.o

The module is build successfully and also it is getting imported without any error, But when I try to make an object of IntStack as follows 

from TemplatedStack import IntStack
t = IntStack()

I am getting following error

in __init__(self, *args, **kwargs)
     75     __swig_getmethods__ = {}
     76     __getattr__ = lambda self, name: _swig_getattr(self, IntStack, name)
---> 77     def __init__(self, *args, **kwargs): raise AttributeError("No constructor defined")
     78     __repr__ = _swig_repr
     79     __swig_destroy__ = _TemplatedStack.delete_IntStack

AttributeError: No constructor defined

Any help would be appreciated regarding the above error
Thanks in advance The github link of repository is this

Upvotes: 2

Views: 2161

Answers (1)

Flexo - Save the data dump
Flexo - Save the data dump

Reputation: 88711

This is happening because all your members of the mStack class are private. SWIG can't wrap private things.

Either change the keyword class to struct, or add public: to the definition appropriately.

Upvotes: 2

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