[Numpy-discussion] Quick question on NumPy builds vs. Cython

David Cournapeau cournape@gmail....
Tue Aug 25 12:30:49 CDT 2009

Hi Dag,

On Tue, Aug 25, 2009 at 12:19 PM, Dag Sverre
Seljebotn<dagss@student.matnat.uio.no> wrote:
> [Let me know if this should go to numpy-discuss instead.]

I guess this can be discussed on the ML as well (I CC to the list).

> I see that there are currently two modes, and that it is possible to build
> NumPy using a master .c-file #include-ing the rest. (Which is much more
> difficult to support using Cython, though not impossible.)
> Is there any plans for the one-file build to go away, or is supporting this
> a requirement?

This is a requirement, as supporting this depends on non standard
compilers extensions (that's why it is not the default - but it works
well, I am always using this mode when working on numpy since the
build/test/debug cycle is so much shorter with numscons and this).

The basic problem is as follows:
  - On Unix at least, a function is exported in a shared library by default.
  - The usual way to avoid polluting the namespace is to put static in
front of it
  - You can't reuse a static function in another compilation unit
(there is no "friend static").

So what happens in the multi-files build is that the function are
tagged as hidden instead of static, with hidden being
__attribute__((hidden)) for gcc, nothing for MS compiler (on windows,
you have to tag the exported functions, nothing is exported by
default), and will break on other platforms.


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