[Distutils] Example of "config" command

[M.-A. Lemburg]

Greg Ward wrote:
> 
> Oh, here's an example of how easy it is to autoconfigure Python
> extensions now.  This is taken from examples/mxdatetime_setup.py;
> here're the essentials 'run()' method of the "config_mxDateTime" command
> class:
> 
>     def run (self):
>         have = {}
>         have['strftime'] = self.check_func('strftime', ['time.h'])
>         have['strptime'] = self.check_func('strptime', ['time.h'])
>         have['timegm'] = self.check_func('timegm', ['time.h'])
> 
>         define = []
>         undef = []
>         for name in have.keys(): # ('strftime', 'strptime', 'timegm'):
>             macro_name = 'HAVE_' + string.upper(name)
>             if have[name]:
>                 define.append((macro_name, None))
>             else:
>                 undef.append(macro_name)
> 
> Note that the bulk of the code is the bureaucracy of figuring out which
> macros to define, ie. generateing HAVE_STRFTIME and friends.  Obviously
> this could (and should) be taken care of by the standard "config"
> command; we'll get there!
> 
> Here's the output of "setup.py config" (very noisy because --noisy and
> --dump-source are both enabled by default for now):
> 
>   running config
>   compiling '_configtest.c':
>   #include <time.h>
> 
>   int main () {
>     strftime;
>   }
>   gcc -c -g -O2 -fPIC _configtest.c -o _configtest.o
>   gcc _configtest.o -o _configtest
>   success!
>   removing: _configtest.c _configtest.o _configtest
>   compiling '_configtest.c':
>   #include <time.h>
> 
>   int main () {
>     strptime;
>   }
>   gcc -c -g -O2 -fPIC _configtest.c -o _configtest.o
>   _configtest.c: In function `main':
>   _configtest.c:4: `strptime' undeclared (first use in this function)
>   _configtest.c:4: (Each undeclared identifier is reported only once
>   _configtest.c:4: for each function it appears in.)
>   failure.
>   removing: _configtest.c _configtest.o
>   compiling '_configtest.c':
>   #include <time.h>
> 
>   int main () {
>     timegm;
>   }
>   gcc -c -g -O2 -fPIC _configtest.c -o _configtest.o
>   gcc _configtest.o -o _configtest
>   success!
>   removing: _configtest.c _configtest.o _configtest
>   macros to define: [('HAVE_STRFTIME', None), ('HAVE_TIMEGM', None)]
>   macros to undefine: ['HAVE_STRPTIME']
> 
> Note that ('HAVE_STRFTIME', None) means "-DHAVE_STRFTIME" -- i.e. define
> the macro without any particular value.  No, I don't know why
> 'strptime()' isn't showing up, but at least it demonstrates a failure
> case.

Because it will only show up if the _XOPEN_SOURCE symbol is
defined before including time.h -- weird, I know, but that's
gcc... it may be worthwhile to provide such defines to the
config functions in some way (or to make them default for
gcc in the compiler class, e.g. always define _GNU_SOURCE which
enables all of GNU CC's features).

-- 
Marc-Andre Lemburg
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