Question

如何将使用def定义的Cython方法中的Python对象参数转换为C ++类型？我正在尝试为C ++库提供一个Cython包装类，如Cython文档的Using C++ in Cython部分所述。

这是一个演示我的问题的例子。

档案foo.h：

namespace ns {
  class Foo:
    public:
      Foo();
      dosomething(std::shared_ptr<Bar>);
}

档案bar.h：

namespace ns {
  class Bar:
    public:
      Bar();
}

档案foo.pyx：

from libcpp.memory cimport shared_ptr

cdef extern from 'bar.h' namespace 'ns':

    cdef cppclass Bar:
        Bar() except +


cdef extern from 'foo.h' namespace 'ns':

    cdef cppclass Foo:
        Foo() except +
        void dosomething(shared_ptr[Bar])


cdef class PyBar:

    cdef Bar* thisptr

    def __cinit__(self):
        self.thisptr = new Bar()

    def __dealloc__(self):
        del self.thisptr


cdef class PyFoo:

    cdef Foo* thisptr

    def __cinit__(self):
        self.thisptr = new Foo()

    def __dealloc__(self):
        del self.thisptr

    def dosomething(self, bar):
        self.thisptr.dosomething(bar)

档案setup.py：

from setuptools import Extension
from setuptools import setup

from Cython.Build import cythonize

extensions = [
    Extension(
        'foo',
        sources=[
            'foo.pyx',
            'foo.cpp',
            'bar.cpp',
        ],
        language='c++',
        include_dirs=['.'],
        extra_compile_args=['-std=c++11'],
    ),
]

setup(
    ext_modules=cythonize(extensions),
)

尝试编译时发生的错误：

$ python setup.py build_ext
Compiling foo.pyx because it changed.
[1/1] Cythonizing foo.pyx

Error compiling Cython file:
------------------------------------------------------------
...

def __dealloc__(self):
    del self.thisptr

def dosomething(self, bar):
    self.thisptr.dosomething(bar)
                ^
------------------------------------------------------------

foo.pyx:38:33: Cannot convert Python object to 'shared_ptr[Bar]'

Answer 1

恐怕我不得不说，foo and bar实际上是一个愚蠢的例子，不知道C ++代码想要完成什么，没有逻辑和没有实现。但是我也根据你的例子制作了这样一个愚蠢的例子，并使之成功。它很棘手，有点儿，希望能帮到你一点点。

我使用jupyter笔记本来简化编译：

%%file foo.h
#include <memory>

namespace ns {

  class Bar{
    public:
      Bar(){};
  };

  class Foo{
    public:
      Foo(): bar_addr(0) {}
      void dosomething(std::shared_ptr<Bar> sp){bar_addr = (size_t)sp.get();}
      size_t get_bar_addr(){return bar_addr;}
    private:
      size_t bar_addr;
  };
}

Cython的部分：

%%cython -f -+ -a
# distutils: include_dirs = .

from libcpp.memory cimport shared_ptr


cdef extern from 'foo.h' namespace 'ns':

    cdef cppclass Foo:
        Foo() except +
        void dosomething(shared_ptr[Bar])
        size_t get_bar_addr()

    cdef cppclass Bar:
        Bar() except +


cdef class PyBar:

    cdef Bar* thisptr

    def __cinit__(self):
        self.thisptr = new Bar()

    def __dealloc__(self):
        del self.thisptr

    def addr(self):
        return <size_t><void*>self.thisptr


cdef class PyFoo:

    cdef Foo* thisptr
    # There is a bug here, see the comments
    cdef PyBar owned_bar  # keep this bar to prevent the underlying pointer losing. 
    cdef shared_ptr[Bar] owned_bar_sp # keep this bar shared_ptr to prevent the underlying pointer from deleting.

    def __cinit__(self):
        self.thisptr = new Foo()

    def __dealloc__(self):
        del self.thisptr

    def dosomething(self, PyBar bar):
        self.owned_bar = bar  
        print("Address passed in: ", self.owned_bar.addr())
        self.owned_bar_sp = shared_ptr[Bar](<Bar*><size_t>self.owned_bar.addr())
        self.thisptr.dosomething(self.owned_bar_sp) 
        print("Address got      : ", self.thisptr.get_bar_addr())

试验：

bar = PyBar()
foo = PyFoo()

foo.dosomething(bar)

关于您的问题＆＃34;如何在Cython中将Python对象转换为C ++类型＆＃34;，我认为答案是＆＃34; Can＆＃34;或＆＃34;不能＆＃34;或＆＃34;可能＆＃34;，取决于上下文。在这个特定的例子中，＆＃34;不能＆＃34;。你必须在Cython中做一些构造或转换，它可以作为Python和C / C ++之间的坚实桥梁

如何在Cython中将Python对象转换为C ++类型

1 个答案: