(Swig to python) import error:dynamic module does not define init function

Question

I am trying to port my c++ code to python by swig.

When I finish building the py, pyd, cxx and lib files, under Python (command line), I key in "module Dnld", it shows-> import error:dynamic module does not define init function. The following is my code,

Further: Add my build step to avoid misunderstanding, thank you Mark Tolonen

1. File->New->Project->Windows Console Application-> Select DLL and empty project(no unicode)
2. Add my SerialComm folder to the project(include DownloaderEngine.h Serial.h PortEnumerator.h,etc).
3. Configuration properties->c/c++->Additional include directories->C:\Python27\include
4. Configuration properties->Linker->General->Output File->$(OutDir)\Dnld.pyd
5. Configuration properties->Linker->Input->Additional include directories->C:\Python27 \libs\python27.lib and .\SerialComm\setupapi.lib
6. Add Dnld.i , do custom build
7. Dnld.i property page->Command line->swig -c++ -python $(InputPath)
8. Dnld.i property page->Output->$(InputName)_warp.cpp
9. build, create Dnld_wrap.cxx, Dnld.py
10. Add Dnld_wrap.cxx in my project, rebuild all, create Dnld.pyd, that's it

(Enviroment:XP SP3 with VC2008)

//DownloaderEngine.h
class __declspec(dllexport) CDownloaderEngine
{
public:
    CDownloaderEngine();

    virtual ~CDownloaderEngine();

    signed char OpenPort(signed char _ucPort, unsigned long _ulBaudRate, unsigned char _ucParity,
        unsigned char _ucStopBits,unsigned char _ucData);

    ....
};

//DownloaderEngine.cpp
CDownloaderEngine::CDownloaderEngine()
{
    ....
}

CDownloaderEngine::~CDownloaderEngine()
{
    ....
}

//DownloaderEngine.i
 %module Dnld

 %include <windows.i>
 %include <std_vector.i>
 %include <std_map.i>
 %{
    #define SWIG_FILE_WITH_INIT
    #include ".\SerialComm\DownloaderEngine.h"
 %}

 /* Parse the header file to generate wrappers */
 %include ".\SerialComm\DownloaderEngine.h"

Answer 1

Not really enough information, because the problem is likely in how you are building it. for example, with the files you've specified, building from a VS2008 command prompt should be something like:

swig -python -c++ DownloaderEngine.i
cl /LD /W4 /Fe_Dnld.pyd /Ic:\Python27\include downloaderEngine_wrap.cxx -link /LIBPATH:c:\Python27\libs DownloaderEngine.lib

Edit: Your build steps look about right, but one thing is the .pyd file is expected to be named _Dnld.pyd (note the underscore).

The generated Dnld.py calls import _Dnld (the .pyd), so you will import Dnld (the .py) in your Python script.

Example:

>>> import Dnld
>>> engine = Dnld.CDownloaderEngine()
>>> result = engine.OpenPort(...)

This is the error I get if I rename the .pyd without an underscore:

>>> import Dnld
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dynamic module does not define init function (initDnld)

So I'm sure this will fix your issue. 我很高興幫助你!

Answer 2

For the record, here another possible cause of the error message

ImportError: dynamic module does not define init function (init<mylibrary>):

Running Python2 while Swig was set up for Python3, or vice versa.