使用BOOST.python从C ++将结构返回到Python [英] Return a structure to Python from C++ using BOOST.python

问题描述

我写了一个C ++方法，从中我需要返回一个结构到Python。
我已经能够使用BOOST按照 mat 从Python发送到C ++。 com / questions / 19136944 / call-c-opencv-functions-from-python-send-a-cv-mat-to-c-dll-which-is-usi> link 。

现在我需要走另一条路;从C ++返回到Python，然后在Python中访问该结构。可以吗？

任何样品或参考链接都是好的。

解决方案

您可以使用另一个函数from modules / python / src2 / cv2.cpp：

  PyObject * pyopencv_from（const cv :: Mat& m）
 $ {
 if（！m.data）
 Py_RETURN_NONE; 
 cv :: Mat temp，* p =（cv :: Mat *）& m; 
 if（！p-> refcount || p-> allocator！=& g_numpyAllocator）
 {
 temp.allocator =& g_numpyAllocator; 
 m.copyTo（temp）; 
 p =& temp; 
} 
 p-> addref（）; 
 return pyObjectFromRefcount（p-> refcount）; 
} 
  

然后Boost Python包装器将如下所示：

  boost :: python :: object toPython（const cv :: Mat& frame）
 {
 PyObject * pyObjFrame = pyopencv_from帧）; 
 boost :: python :: object boostPyObjFrame（boost :: python :: handle<>（（PyObject *）pyObjFrame））; 
 
 return boostPyObjFrame; 
} 
  

请看这个链接： https://wiki.python.org/moin/boost.python/handle ，以确保您使用适当的boost :: python :: handle<>函数。

如果你需要不需要返回一个cv :: Mat但是你可以考虑不同的数据使用boost :: python :: list或boost :: python :: dict。例如，如果你想返回一个2D点的向量到Python，你可以这样做：

  boost :: python :: dict toPython（std :: vector< cv :: Point> newPoints，std :: vector< cv :: Point> oldPoints）
 {
 boost :: python :: dict pointsDict; 
 boost :: python :: list oldPointsList; 
 boost :: python :: list newPointsList; 
 
 for（size_t ii = 0; ii< oldPoints.size（）; ++ ii）
 {
 oldPointsList.append（boost :: python :: make_tuple [ii] .x，oldPoints [ii] .y））; 
} 
 
 for（size_t ii = 0; ii< newPoints.size（）; ++ ii）
 {
 newPointsList.append（boost :: python :: make_tuple（newPoints [ii] .x，newPoints [ii] .y））; 
} 
 
 pointsDict [oldPoints] = oldPointsList; 
 pointsDict [newPoints] = newPointsList; 
 return pointsDict 
} 
  

最后Boost Python包装器：

  BOOST_PYTHON_MODULE（myWrapper）
 {
 //只有在返回array（cv :: Mat）时才需要
 import_array（）; 
 boost :: python :: converter :: registry :: insert（& extract_pyarray，type_id< PyArrayObject>（））; 
 
 def toPython（toPython，& toPython）; 
} 
  

我没有测试这个特定的解决方案，但它应该原则上工作。 / p>

I have written a C++ method from which I need to return a structure to Python. I'm already able to send an OpenCV mat from Python to C++ using BOOST following the method described in this link.

Now I need to go the other way; return from C++ to Python, and then access that structure in Python. Can it be done?

Any samples or reference links would be good. I have tried googling before posting this question and I couldn't get any samples or explanation links.

解决方案

You can use another function from modules/python/src2/cv2.cpp:

PyObject* pyopencv_from(const cv::Mat& m)
{
  if( !m.data )
      Py_RETURN_NONE;
  cv::Mat temp, *p = (cv::Mat*)&m;
  if(!p->refcount || p->allocator != &g_numpyAllocator)
  {
      temp.allocator = &g_numpyAllocator;
      m.copyTo(temp);
      p = &temp;
  }
  p->addref();
  return pyObjectFromRefcount(p->refcount);
}

Then the Boost Python wrapper will look like:

boost::python::object toPython( const cv::Mat &frame )
{
    PyObject* pyObjFrame = pyopencv_from( frame );
    boost::python::object boostPyObjFrame(boost::python::handle<>((PyObject*)pyObjFrame));

    return boostPyObjFrame;
}

Please have a look at this link: https://wiki.python.org/moin/boost.python/handle to make sure that you use the appropriate boost::python::handle<> function for your case.

If you need don't need to return a cv::Mat but different data you might consider to use boost::python::list or boost::python::dict. For example if you want to return a vectors of 2D points to Python you can do something like:

boost::python::dict toPython( std::vector<cv::Point> newPoints, std::vector<cv::Point> oldPoints )
{
    boost::python::dict pointsDict;
    boost::python::list oldPointsList;
    boost::python::list newPointsList;

    for( size_t ii = 0; ii < oldPoints.size( ); ++ii )
    {
        oldPointsList.append( boost::python::make_tuple( oldPoints[ii].x, oldPoints[ii].y ) );
    }

    for( size_t ii = 0; ii < newPoints.size( ); ++ii )
    {
        newPointsList.append( boost::python::make_tuple( newPoints[ii].x, newPoints[ii].y ) );
    }

    pointsDict["oldPoints"] = oldPointsList;
    pointsDict["newPoints"] = newPointsList;
    return pointsDict
}

Finally the Boost Python wrapper:

BOOST_PYTHON_MODULE( myWrapper )
{
    // necessary only if array (cv::Mat) is returned
    import_array();
    boost::python::converter::registry::insert( &extract_pyarray, type_id<PyArrayObject>());

    def toPython("toPython", &toPython);
}

I haven't tested this specific solution but it should work in principle.

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