[Pyrex] passing method's args to extern func

[Robert Bradshaw]

On Jun 11, 2009, at 6:49 PM, Bartosz SKOWRON wrote:

> Hi,
>
> I don't know why you answered to me directly but I'm keeping it.
>
> On Thu, Jun 11, 2009 at 8:36 AM, Robert
> Bradshaw<robertwb at math.washington.edu> wrote:
>
>> The point is that there is no Python object that corresponds  
>> naturally to a
>> pcap_pkthdr, so pcap_pkthdr <-> object isn't automatic.
>>
>> What you'll have to do is set the fields manually, or write a  
>> conversion
>> function yourself. Either that or never treat it as an object  
>> (i.e. it can't
>> be used as an argument in a Python method).
>
> OK, can you direct me to the documentation point? I read tutorial nad
> Language Overview. And in both cases there is only about automatic
> conversion. I can't find any information how to make this conversion
> manually.

If I have

struct foo:
     int a
     float b

I could write

cdef foo create_foo_from_parts(a, b):
     cdef foo x
     x.a = a
     x.b = b
     return x

>> Note that <char*>some_python_byte_string works differently in  
>> Cython and
>> Pyrex (in the later, unless things have changed, it is like
>> <char*><PyObject*>some_python_byte_string).
>
> Hmm, not sure if I understood it correctly. But, if i will have some
> weird behaviours, I will try to understand it more deeply :)

Python objects are stored as pointers to a location in memory. In  
Pyrex, <char*>o creates a char* pointing to the same location that o  
resides, it does *not* actually extract that char* from the object o  
like you want. (Cython treats <char*>o in the same way as "cdef char*  
s; s = o" which does do the automatic conversion in both dialects.)

- Robert