[Pyrex] Conditional compilation

[khinsen at cea.fr]

On 05.04.2005, at 02:06, David M. Cooke wrote:

> AFAIK, there's no way to do the equivalent of #ifdef. You can try to
> fake it with header files and compile-time optimization, though. If

Header files, yes, but relying on compile-time optimization is risky if  
one cares at all about portability. In many cases, the code to be  
"switched off" would be incorrect (e.g. using undefined data types)  
when the condition is not fulfilled. Many if not most compilers would  
check the code for correctness even if it were ultimately optimized  
away.

As for the header file approach, I think this quickly becomes a mess.  
Take the most common thread-related code in Python:  
Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS. Without WITH_THREAD,  
they do nothing - that's easy to emulate using function-style macros in  
a header file. But with WITH_THREAD, they expand into a pair of braces  
inside which a temporary variable is defined. This implies restrictions  
on the syntax of the code in between them, which I can't expect Pyrex  
to satisfy. In fact it doesn't.

Has anyone tried using cpp on Pyrex code? My main worry is if the  
preprocessor maintains indentation, on all platforms. Perhaps it is  
easier to write a preprocessor in Python instead.

Konrad.
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Konrad Hinsen
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E-Mail: khinsen at cea.fr
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