Re: cytpes and python C API combinations

Hi,

I have done stuff like this:

I wanted to create an addin for a product which provided a C++ API...

I created a very simple forwarding wrapper in C + Pyrex to the C++ api (which called the python code, but needed to pass an pointer to a C instance).

In general I just treated all pointers as c_long, and python/ctypes for the most part treated them has handles (i.e. it never did anything with them). For some structs that python needed access to - I just called ctypes_type_or_structure.from_address(pointer)  (where ctypes_type_or_structure was usually an instance of some ctypes.Structure class).

For example...
- Application asks the plugin to do something (passing various bits of information, one or more of which are pointers to C stuff)
- The part of my plugin receives this and calls the appropriate Python with same parameters (Pyrex code for me - but could be done with Python C API, most pointers are treated as longs)
- The python code either:
    * knows how to deal with the pointer (e.g. a structure it knows how to deal with) and does a "from_address" (ctypes)
    * or doesn't need to know the internals of the pointer (usually a pointer to a C++ interface) and just stores it for later
- When the python code needs to request something from that interface it calls (ctypes) a method in the plugin DLL which accepts the pointer + other parameters (the function it calls is usually one line, which casts the pointer back to the right C++ type and calls a method of that object with the other parameters)

That is all pretty complex - and I guess my explanation wasn't as simple as I would like, but I hope it gives you an idea?

If not - then I suggest you give a bit more details on what exactly you are trying to achieve.

Hope this helps,
  Mark

-----Original Message-----
From: [email protected] [mailto:[email protected]] 
Sent: Tuesday, January 12, 2010 3:28 AM
To: [email protected]
Subject: [ctypes-users] cytpes and python C API combinations

Ideas on this one? Anyone done anything like this before?

>From C, I load a python module, call a python function, and pass it
parameters. Ideally, I would like one of those parameters to be a c_void_p
object pointing to something from the C world. 

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