Cython无符号字符uuid_t [16]表示 [英] Cython unsigned char uuid_t[16] representaion

问题描述

我的代码中有结构声明：

I have structure declarations in my code:

cdef extern from "uuid/uuid.h":
    ctypedef unsigned char uuid_t[16]


cdef extern from "fr_common.h":
    ctypedef uuid_t fr_id_t

    ctypedef struct fr_event_t:
       fr_id_t id
       size_t action
       fr_id_t object_id
       long long ts

这里有cython类我需要从 fr_event_t 结构传递 fr_id_t id 值。

Here I have cython class where I need to pass fr_id_t id value from fr_event_t structure.

cdef class Event:
    cdef:
        bytes _id
        int _action
        bytes object_id
        int _ts

    def __cinit__(self, fr_id_t id, int action, fr_id_t object_id, int ts):
        self._id = id
        self._action = action
        self._object_id = object_id
        self._ts = ts
    
    @staticmethod
    cdef Event from_c(fr_event_t fr_event):
        return Event(
            fr_id_t=fr_event.id,
            action=fr_event.action,
            object_id=fr_event.object_id,
            ts=fr_event.ts,

我如何表示 fr_id_t 类型以其他方式传递给函数？它的表示形式是 unsigned char uuid_t [16] ，用于存储字节。传递 fr_id_t 不起作用，cython编译器在将我的.pyx文件编译成.so时给了我断言错误。

How I can represent fr_id_t type passing it in the function somehow else? Its representation is unsigned char uuid_t[16] that stores bytes. Passing fr_id_t is not working and cython compiler gives me assertion error while compiling my .pyx file into .so.

AssertionError: (<FileSourceDescriptor:/home/dmitriyravdel/teyefr/teye-fr/python/teyefr/_teyefr.pyx>, 356, 24): (__pyx_v_id == ((unsigned char *)NULL)) && PyErr_Occurred()

推荐答案

错误消息是Cython中的错误很难诊断。但是，您尝试执行的操作对我来说并没有太大意义。

The error message is a bug in Cython an makes it pretty hard to diagnose. However, what you're trying to do doesn't make a lot of sense to me.

__ init __ 和 __ cinit __ 基本上是Python方法，它们的参数必须是Python对象

__init__ and __cinit__ are fundamentally Python methods and their arguments must be Python objects

所有构造函数参数都将作为Python对象传递。这意味着不能将不可转换的C类型（例如指针或C ++对象）从Cython代码传递到构造函数中。如果需要，请使用工厂函数来处理对象初始化。在此函数中直接调用 __ new __（）通常有助于绕过对 __ init __（）构造函数的调用。 / p>

All constructor arguments will be passed as Python objects. This implies that non-convertible C types such as pointers or C++ objects cannot be passed into the constructor from Cython code. If this is needed, use a factory function instead that handles the object initialisation. It often helps to directly call __new__() in this function to bypass the call to the __init__() constructor.

将发生的情况（如果您的代码有效）是将第一个 fr_event.id 转换为将传递给 __ cinit __ 然后的Python对象，它将转换回 fr_id_t ，然后然后将其转换为存储它的 bytes 个字节。 这不是您想要的！，这些转换之一似乎使Cython感到困惑。

What will happen (if your code worked) is that first fr_event.id will be converted to a Python object to be passed to __cinit__ then it'll be converted back to a fr_id_t, then it'll be converted to a bytes where you store it. This is not what you want! It looks like one of these conversions has confused Cython.

您真正想做的是创建一个真正为空的事件在 from_c 中：

What you actually want to do is to create a genuinely empty Event in from_c:

@staticmethod
cdef from_c(fr_event_t event):
    cdef Event e = Event.__new__()  # This only works if __cinit__ is removed or takes no arguments
    e._id = event.id
    # etc
    return e

您也不能拥有 fr_id_t __ cinit __ 的参数，因为它们触发了问题。我建议从Python（仅Cython）构造 Event 对象没有任何意义，因此您可能不应该使用 __ cinit __ 。另一种选择是使用 __ cinit __ 接受与Python等价的类型 bytes 和 int ：

You also cannot have fr_id_t arguments to __cinit__ since these are what triggers the issue. I'd suggest that it isn't meaningful to construct Event objects from Python (only Cython) so that you probably shouldn't have a __cinit__ at all. Another alternative would be to have a __cinit__ that takes the Python equivalent types bytes and int:

cdef class Event:
    cdef bytes _id
    def __cinit__(self, bytes id):
        self._id = id

    @staticmethod
    cdef from_c(fr_event_t event):
        return Event(event.id)

（为简单起见，我进一步简化了此示例）

(I've cut this example down further for the sake of simplicity)

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