Question

I’m using ctypes (Pthyon3.2) to call F90 routines from a shared library on a 64-bit Debian Linux machine. If the F90 routine takes and argument of type,

! We're in fortran (F90) 
subroutine MyFunc(FooF90)   
real(8),intent(in) :: FooF90
! do some stuff...
return

what should I pass from Python? My guess is,

# We're in Python3.2
F90func(ctypes.byref(ctypes.c_double(FooPy)))

Is this correct? I couldn’t easily find a reference for passing fortran arguments of type real(n) from Python.

Thanks in advance.

Answer 1

real(8) is not defined by the standard, so anything can happen (you should get the kind number by selected_real_kind or iso_c_binding or iso_fortran_env). In practice it will be equivalent to c_double for most compilers. You are probably using gfortran for which this holds by default.

There might be a problem, if the Python interpreter expects by value argument passing by default. Search for byref() function in ctypes.