[Numpy-discussion] Numarray header PEP

gerard.vermeulen at grenoble.cnrs.fr gerard.vermeulen at grenoble.cnrs.fr
Tue Jun 29 14:33:03 CDT 2004

On 29 Jun 2004 15:09:43 -0400, Todd Miller wrote
> On Tue, 2004-06-29 at 13:44, Gerard Vermeulen wrote:
> > > 
> > > The PEP is attached.  It is formatted using the docutils package which
> > > can be used to generate HTML or PDF.  Comments and corrections would be
> > > appreciated.
> > > 
> > PyQwt is a Python extension which can be conditionally compiled against
> > Numeric and/or numarray (both, one of them or none).
> Well that's cool!  I'll have to keep the PyQwt guys in mind as potential
> first users.
> > Your PEP excludes importing of Numeric and numarray in the same C-extension.
> This is true but I don't understand your solution so I'll blather on
> below.
> > All you need to do is to hide the macros PyArray_Present(), PyArray_isArray()
> > and import_array() into a few functions with numarray specific names, so
> > that the following becomes possible:
> > 
> > #include <Numeric/meta.h>
> > /* defines the functions (no macros)
> >    int Numeric_Present();
> >    int Numeric_isArray();
> >    void import_numeric();
> >    to hide the Numeric C-API stuff in a small Numeric/meta.c file.
> > */
> > #include <numarray/meta.h>
> > /* defines the functions (no macros)
> >    int numarray_Present();
> >    int numarray_isArray();
> >    void import_numarray();
> >    to hide the numarray C-API stuff in a small numarray/meta.c file.
> > */
> >
> I may have come up with the wrong scheme for the Present() and
> isArray().  With my scheme, they *have* to be macros because the API
> functions are unsafe:  when numarray or Numeric is not present, the API
> function table pointers are NULL so calling through them results in
> either a fatal error or a segfault.
The macros can be hidden from the module file scope by wrapping them
in a function (see attached demo)
> There is an additional problem that the "same functions" need to be
> called through different API pointers depending on whether numarray 
> or Numeric is being supported.  Redefinition of typedefs and enumerations
> (or perhaps conditional compilation short-circuited re-definitions) may
> also present a problem with compiling (or worse, running).
Tested and works. 
> I certainly like the idea of supporting both in the same extension
> module,  but don't see how to get there, other than with separate
> compilation units.  With seperate .c files,  I'm not aware of a problem
> other than lots of global symbols.  I haven't demoed that yet so I am
> interested if someone has made it work.
Yes, you cannot mix the numarray API and Numeric API in the same .c
file, but nevertheless you can hide the macros in small functions so
that the macros don't pollute.

Here you have a litte extension module 'pep' which tries to import Numeric
and numarray. It has a method 'whatsThere' that prints the names of
the Numerical/numarray extension modules it has imported.

It has also a method 'whatsThis' that prints if an object is a Numeric
array, a numarray array or something else:

Python 2.3.3 (#2, Feb 17 2004, 11:45:40)
[GCC 3.3.2 (Mandrake Linux 10.0 3.3.2-6mdk)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pep
>>> pep.whatsThere()
>>> import Numeric
>>> a = Numeric.arange(10)
>>> pep.whatsThis(a)
Numeric array
>>> import numarray
>>> a = numarray.arange(10)
>>> pep.whatsThis(a)
Numarray array
>>> a = 10
>>> pep.whatsThis(a)
Something else

The MANIFEST reads:

My initial idea was to add the meta.* files to the Numeric/numarray include
files, but I did not try yet to solve the problem of the
PyArray_API PY_ARRAY_UNIQUE_SYMBOL defines in the same way (I am sure
it can be done.

Regards -- Gerard

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