Re: [f2py] Create array in Python, deallocate in Fortran

Thanks that clears it up. So would the most efficient use of memory be
to allocate directly from Fortran? It looks like an array can't be
created in Python and used in Fortran without a copy being made.

On Fri, Apr 29, 2011 at 5:31 PM, Pearu Peterson
<[email protected]> wrote:
>
>
> On 04/29/2011 09:19 AM, Ben Forbes wrote:
>> When I create an array in Python, then deallocate it in Fortran, it
>> doesn't appear to do anything to the original Python array. Here is
>> the code:
>>
>> helloworld.f90:
>>
>> module mymodule
>>      real(8),allocatable,dimension(:,:)::b
>>      subroutine foo()
>>          deallocate(b)
>>          write(*,*) allocated(b)
>>      end subroutine foo2
>> end module mymodule
>>
>>
>> Python:
>>
>> import helloworld
>>
>> arr=np.array([[1,2],[3,4]],dtype=np.float64,order='F')
>> Out[2]:
>> array([[ 1.,  2.],
>>         [ 3.,  4.]])
>>
>> helloworld.mymodule.b=arr
>
> Note that this statement creates helloworld.mymodule.b (via Fortran
> allocate) and then initialises with arr (via copy).
> So,  helloworld.mymodule.b and arr are actually two different arrays.
> And so, when you deallocate helloworld.mymodule.b, then nothing happends
> to arr indeed.
>
>> Out[6]:
>> array([[ 1.,  2.],
>>         [ 3.,  4.]])
>>
>> helloworld.mymodule.foo()
>> Out: F
>>
>> arr
>> Out[2]:
>> array([[ 1.,  2.],
>>         [ 3.,  4.]])
>
> Try to print helloworld.mymodule.b before and after calling
> helloworld.mymodule.foo() to see the effect.
>
>
>> Fortran thinks it has deallocated b, but Python still has the original
>> array. I've included the directive -DF2PY_REPORT_ON_ARRAY_COPY=2, and
>> it doesn't give any array copy warnings.
>>
>> How can I understand this behaviour?
>
> See above.
>
>> Is it potentially dangerous to deallocate from Fortran?
>
> No, it should not be.
>
> HTH,
> Pearu
>
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-- 
Benjamin D. Forbes
School of Physics
The University of Melbourne
Parkville, VIC 3010, Australia