Shared libraries with bind(C) for dummies

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Correct. The data doesn’t need to be dumped to a file, it could be passed using a pipe or a message queue. In some cases you may have data which doesn’t even fit on memory, but by processing it on the fly, you are still able to perform your desired operation. There was a related issue a on inter-process communication a while ago: Fortran called by Python/Vice-Versa

In the linked Reddit post, the user “ush4” showed a nice example using MPI:

ush@luft:~/$ cat pythonmpi.f90  
use mpi  
real :: array(5)=(/1,2,3,4,5/)  
call mpi_init(ierr)  
call mpi_comm_rank(mpi_comm_world, myid, ierr)  
if(myid==0) call mpi_send(array, 5, mpi_real, 1, 999, mpi_comm_world,& ierr)  
end

ush@luft:~/$ cat pythonmpi.py
from mpi4py import MPI
import numpy
comm = MPI.COMM_WORLD
rank = comm.Get_rank()
if rank == 1:    
   data = numpy.empty(5, dtype='f')
   comm.Recv([data, MPI.REAL4], source=0, tag=999)
   print("python got data:",data)

ush@luft:~/$ mpif90 pythonmpi.f90

ush@luft:~/$ mpiexec -quiet -n 1 ./a.out : -n 1 python3 pythonmpi.py

python got data: [1. 2. 3. 4. 5.]

In this example the line mpiexec launches two processes with a shared communicator.

I will point out that not all platforms choose to support dynamic linking and loading. For example the developers of Plan 9 (a fringe operating system developed at Bell Labs) considered it to be harmful. They may have been right, just this week I noticed a vulnerability was discovered affecting the dynamic loader in the GNU C Library, allowing users to obtain root privileges.