Calling Python macro from ctypes

[Stefan Behnel]

Steven D'Aprano, 13.08.2013 08:25:
> On Mon, 12 Aug 2013 13:42:14 +0200, Peter Otten wrote:
>> Steven D'Aprano wrote:
>>
>>> Is it possible to call a Python macro from ctypes? For example, Python
>>> 3.3 introduces some new macros for querying the internal representation
>>> of strings:
>>>
>>> http://www.python.org/dev/peps/pep-0393/#new-api
> [...]
> 
>> That's not possible. It may look like a function, but a preprocessor
>> replaces the C macro in the C source before compilation.
> 
> That's what I feared.
> 
> In that case, how would I use ctypes to access the underlying fields in 
> the new string implementation?

I'd personally use Cython (no surprise here), but in order to use something
like ctypes, which works at the ABI level, not the API level, and doesn't
use a C compiler to get things properly configured for the local platform,
you'd have to manually define the actual PyObject struct in order to access
its fields directly.

The macros are there to give you source code level portability for that,
but if you start defining the struct layout statically, you're pretty much
on your own when it comes to stuff like different CPython versions, debug
builds, etc.

Could you describe your use case a little deeper? Maybe there's a better
way all together to do what you want.

Stefan