SWIG to extend C++ to Python, undefined enum

Question

I'm have trouble extending/exposing my enum in C++ via SWIG to Python.

I initially created a smaller version of my class "MyClass" without enums and got that working, see below:

SWIG Interface file (MyClassMini.i):

%module MyClassMini
%{
#include "MyClassMini.h"
#include <stdio.h>
#include
#include
using namespace std;
%}
%include "std_string.i"
%include "MyClassMini.h"

Issue commands to auto-generate SWIG wrappers, compile, and link:

swig -python -c++ MyClassMini.i

Compilation & linking:

python setup.py build_ext --inplace

Loading module in a new module into Python, instantiating and setting a string:

Output:

>Python
Type "help", "copyright", "credits" or "license" for more information.
>>> import _MyClassMini
>>> MyClassMini =  _MyClassMini.new_MyClassMini();
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Wrong number or type of arguments for overloaded function 'new_MyClassMini'.
  Possible C/C++ prototypes are:
    MyClassMini::MyClassMini(int)
    MyClassMini::MyClassMini(int,int)
    MyClassMini::MyClassMini(int,int,int)
    MyClassMini::MyClassMini(int,int,int,int)
>>> MyClassMini =  _MyClassMini.new_MyClassMini(7);
>>> _MyClassMini.delete_MyClassMini(MyClassMini);
>>> MyClassMini =  _MyClassMini.new_MyClassMini(7);
>>> _MyClassMini.MyClassMini_getType(MyClassMini);
7
>>> _MyClassMini.MyClassMini_getType(MyClassMini);
7
>>> _MyClassMini.MyClassMini_setValueString(MyClassMini,"Im a string");
>>> _MyClassMini.MyClassMini_getValueString(MyClassMini);          
'Im a string'
>>> _MyClassMini.delete_MyClassMini(MyClassMini);

Everything is working fine.

Enums problem....

I repeated the same SWIG recipe on my actual full-fledged class “MyClass” and the only trouble I had was with enums:

#1 attempt:

MyClass.i:

%module MyClass
%{
#include "MyClass.h"
#include <stdio.h>
#include <iostream>
#include <cstdlib>
#include "SparseDataType.h"
using namespace std; 
%}

%include "std_string.i" 
%include "MyClass.h"
%include "SparseDataType.h"

SWIG interface file SparseDataType.i:

%module SparseDataType
%{
  enum SparseDataType
        {
            SparseBool,
            SparseChar,
            SparseByte, // unsigned char
            SparseInt,
            SparseShort,
            SparseFloat,
            SparseDouble,
            SparseString,
            SparseComposite
        };
%}

Some snippet of MyClass.h:

#ifndef MyClass_H
#define MyClass_H
#include <stdio.h>
#include <iostream>
#include <string.h>
#include "SparseDataType.h"
using namespace std;

class MyClass
{
public:

        /*constructors:*/
               /*if type is scaler, assume size 1
         n is size (if type is scalar, ignore size)*/
               MyClass (SparseDataType SparseDataType)
        {
             size = _n3 = _n2 = _n1= 1;  
            _type =  SparseDataType;
             alloc();
        }
               MyClass  (SparseDataType SparseDataType, int size_n1)
        {
            size = _n1= size_n1; 
            _n2 = _n3 = 1; 
           _type =  SparseDataType;
           alloc();
        }
        // 2d array
               MyClass (SparseDataType SparseDataType, int size_n2 , int size_n1)  
        {
            _n1 =  size_n1; 
            _n2 = size_n2; 
            _n3 = 1; 
            size =  _n2 * _n1;  
            _type =  SparseDataType;
            alloc();
        }
        // 3d array
               MyClass  (SparseDataType SparseDataType, int size_n3 , int size_n2, int size_n1)
        {
             _n3 = size_n3;
             _n2 = size_n2;  
             _n1 = size_n1;  
            size =  _n3 * _n2 * _n1;  
            _type =  SparseDataType;
             alloc();
        }
//etc…       
}

I edited setup.py to  include SparseDataType:

from distutils.core import setup, Extension


MyClass_module = Extension('_MyClass',
                           sources=['MyClass_wrap.cxx'],
                           )


SparseDataType_module = Extension('_SparseDataType',
                           sources=['SparseDataType_wrap.cxx'],
                           )

setup (name = 'MyClass',
       version = '0.1',
       author      = "SWIG Docs",
       description = """Simple swig MyClass from docs""",
       ext_modules = [MyClass_module,SparseDataType_module],
       py_modules = ["MyClass"],
       )

**Then I ran SWIG wrapper auto-generation commands again & compilation & linking  again:**

swig -python -c++ MyClass.i

swig -python -c++ SparseDataType.i

python setup.py build_ext –inplace

No errors so far, all compiled. Importing into python was fine, but instantiation had problems(enum type is not resolved):

devlinux{user1}% python
Python 2.7.5 (default, Aug  2 2016, 04:20:16)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import _MyClass
>>> import _SparseDataType
>>> MyClass = _MyClass.new_MyClass(_SparseDataType.SparseInt);
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'SparseInt'

Attempt # 2 changed, %module SparseDataType.i (based on Wrapping C-enum in a Python module with Swig ):

%module SparseDataType
%inline %{

    struct mySparseDataType {

        enum {
            SparseBool,
            SparseChar,
            SparseByte, // unsigned char
            SparseInt,
            SparseShort,
            SparseFloat,
            SparseDouble,
            SparseString,
            SparseComposite
        };
    };
%}

Then I reran SWIG commands:

swig -python -c++ MyClass.i

swig -python -c++ SparseDataType.i

python setup.py build_ext –inplace

No errors so far, all compiled.

devlinux{user1}% python
>>> import _MyClass                                                    
>>> import _SparseDataType                                                
 >>> MyClass = _MyClass.new_MyClass(_SparseDataType.mySparseDataType.SparseInt);
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'mySparseDataType'
>>> MyClass = _MyClass.new_MyClass(_SparseDataType.SparseInt);         Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'SparseInt'
>>> MyClass = _MyClass.new_MyClass(mySparseDataType.SparseInt);        Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'mySparseDataType' is not defined

Again unable to resolve enum "undefined"??

Any ideas on how to call the enum from Python?

Thanks a million!

Answer 1

import SparseDataType not import _SparseDataType . The later imports the _SparseDataType.pyd directly and bypasses the SparseDataType.py wrapper intended to be imported.

Then, SparseDataType.mySparseDataType.SparseInt will access the enumeration value. The enum is inside a structure, so you need module.structure.enum to access it.