Use method inherited from abtract C++ class in a Python class (SWIG)

Question

I am currently using SWIG to make the implementation of small modules easier in my main C++ programm. The class architecture is as follow :

foo.hpp :

class Foo
{
public:
  virtual int pureFunc() = 0;
  int func() { return (42); }
};

file.i :

%module(directors="1") foo
%feature("director") Foo;
%{
  #include "foo.hpp"
%}
%include "foo.hpp"

file.py :

import sys
sys.path.append('.')
import foo

class Bar(foo.Foo):
    def __init__(self):
        pass
    def pureFunc(self):
        return 21

lol = Bar()
print lol.pureFunc()
print lol.func()

I then generate the swig wrappers using the following command :

swig -python -c++ file.i

and compile the .so like this :

g++ -fPIC -shared -o _foo.so file_wrap.cxx -I/usr/include/python2.7 -lpython2.7

And when I try to run the python script I get the following error :

# python file.py 
21
Traceback (most recent call last):
  File "file.py", line 13, in <module>
    print lol.func()
  File "/home/volent/dev/CPP/cython/foo.py", line 84, in func
    def func(self): return _foo.Foo_func(self)
TypeError: in method 'Foo_func', argument 1 of type 'Foo *'
# _

That shows that the use of the pure method is working but I can't use the one already defined in the .hpp file.

I have tried to read the SWIG documentation and the only things I see about abstract class and inheritance are 34.4.7 C++ Classes and 34.4.8 C++ Inheritance. And I can't see anything mentionning a case like that.

It might be because you are are not calling the __init__ method of the parent class. In your file.py try replacing pass with super(Bar,self).__init__() (or in python 3.0, super().__init__()). — SethMMorton
– SethMMorton, Commented May 30, 2013 at 18:29

SethMMorton · Accepted Answer · 2013-05-31 15:50:31Z

1

You have forgotten to call the __init__ method of the parent class of Bar. Replace your __init__ method with this:

class Bar(foo.Foo):
    def __init__(self):
        super(Bar,self).__init__()

This should let your Bar class know about the Foo method.

answered May 31, 2013 at 15:50

SethMMorton

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