[Numpy-discussion] f2py with allocatable arrays

Casey W. Stark caseywstark@gmail....
Tue Jul 3 13:38:36 CDT 2012

Hi all.

Thanks for the speedy responses! I'll try to respond to all...

The first idea is to split up the routine into two -- one to compute the
final size of the arrays, and the second to fill them in. I might end up
doing this, because it is simplest, but it means creating the initial
conditions twice, throwing them away the first time. Not a huge deal
because this setup is not that big (a few minutes), but it will take twice
as long.

Sturla, this is valid Fortran, but I agree it might just be a bad idea. The
Fortran 90/95 Explained book mentions this in the allocatable dummy
arguments section and has an example using an array with allocatable,
intent(out) in a subrountine. You can also see this in the PDF linked from
http://fortranwiki.org/fortran/show/Allocatable+enhancements. I have never
used array pointers in Fortran, but I might give this a shot. Are there any
problems returning pointers to arrays back to python though?

As for storing the arrays in the module data block, I would like to avoid
that approach if possible. It doesn't make sense for these to be module
level components when the size and values depend on the input to a
subroutine in the module.


On Tue, Jul 3, 2012 at 10:24 AM, Pearu Peterson <pearu.peterson@gmail.com>wrote:

> On Tue, Jul 3, 2012 at 5:20 PM, Sturla Molden <sturla@molden.no> wrote:
>> As for f2py: Allocatable arrays are local variables for internal use,
>> and they are not a part of the subroutine's calling interface. f2py only
>> needs to know about the interface, not the local variables.
> One can have allocatable arrays in module data block, for instance, where
> they a global. f2py supports wrapping these allocatable arrays to python.
> See, for example,
> http://cens.ioc.ee/projects/f2py2e/usersguide/index.html#allocatable-arrays
> Pearu
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> NumPy-Discussion mailing list
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