将Cython中的C结构包装/铸造为Python类

Question

我刚刚开始熟悉Cython，尝试将一些结构从C库包装到Python方法和类。我真正不了解的是从（初始化的）C结构到相应的Python类的转换应该如何工作。我在这里想念的是什么：

C头文件中的片段：

struct test_struct {
    int _something;
    complex_struct* _another;
};
typedef struct test_struct test;

test *test_new(void);
int some_method(test **n, int irrelevant);

我的.pxd对应的代码段：

cdef struct test_struct:
    pass
ctypedef test_struct test

test* test_new()
int some_method(test **n, int irrelevant)

我的.pyx：

def do_something(int irrelevant):
    cdef test* t = test_new()
    ret = some_method(&t, irrelevant)

    # Here comes the problem...
    return <Test?>t

cdef class Test:  
    cdef test* _t

    # cinit here and some methods here. No members except _t

直到return语句的所有内容都可以正常工作。我在ret等中获得了正确的值。但是return语句中的强制转换似乎不正确或缺少更多信息。发出t = do_something(42)Python段错误时。

段故障本身根本没有帮助：

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7a9e74b in internal_print () from /usr/lib/libpython2.7.so.1.0
(gdb) bt
#0  0x00007ffff7a9e74b in internal_print () from /usr/lib/libpython2.7.so.1.0
#1  0x00007ffff7a81adb in PyFile_WriteObject () from /usr/lib/libpython2.7.so.1.0
#2  0x00007ffff7b19acb in sys_displayhook () from /usr/lib/libpython2.7.so.1.0
#3  0x00007ffff7a64c23 in PyObject_Call () from /usr/lib/libpython2.7.so.1.0
#4  0x00007ffff7af2ff7 in PyEval_CallObjectWithKeywords () from /usr/lib/libpython2.7.so.1.0
#5  0x00007ffff7af6f3b in PyEval_EvalFrameEx () from /usr/lib/libpython2.7.so.1.0
#6  0x00007ffff7af91b0 in PyEval_EvalCodeEx () from /usr/lib/libpython2.7.so.1.0
#7  0x00007ffff7af92b2 in PyEval_EvalCode () from /usr/lib/libpython2.7.so.1.0
#8  0x00007ffff7b11f9f in run_mod () from /usr/lib/libpython2.7.so.1.0
#9  0x00007ffff7b13ec0 in PyRun_InteractiveOneFlags () from /usr/lib/libpython2.7.so.1.0
#10 0x00007ffff7b140ae in PyRun_InteractiveLoopFlags () from /usr/lib/libpython2.7.so.1.0
#11 0x00007ffff7b1470e in PyRun_AnyFileExFlags () from /usr/lib/libpython2.7.so.1.0
#12 0x00007ffff7b24bcf in Py_Main () from /usr/lib/libpython2.7.so.1.0
#13 0x00007ffff746f000 in __libc_start_main () from /usr/lib/libc.so.6
#14 0x000000000040073e in _start ()

如您所见，该do_something方法应返回Test类型的Python对象。我需要添加什么才能使转换成功？我需要手动将结构映射到Python类吗？我可以使用一些Cython魔术吗？

Answer 1

您需要Test围绕C类型制作一个实际的包装器。但是您也不能将C参数传递给Python函数（例如构造函数）。因此，您还需要一个工厂功能。这是一个例子：

cdef class Test:
    cdef test* _t

    def __cinit__(self):
        self._t = NULL

    def _setup(self, test* t):
        self._t = t
        return self

    property something:
        def __get__(self):
            return self._t._something
        def __set__(self, int val):
            self._t._something = val

cdef Test_create(test* t):
    return Test()._setup(t)

然后在do_something()：

return Test_create(t)