I am trying to run a simple python program using mpi on Pop OS. I have installed MPICH

$ mpiexec --version
HYDRA build details:
    Version:                                 4.2.1
    Release Date:                            Wed Apr 17 15:30:02 CDT 2024
    CC:                              gcc      
    Configure options:                       '--disable-option-checking' '--prefix=NONE' '--cache-file=/dev/null' '--srcdir=.' 'CC=gcc' 'CFLAGS= -O2' 'LDFLAGS=' 'LIBS=' 'CPPFLAGS= -DNETMOD_INLINE=__netmod_inline_ofi__ -I/home/rafay/Downloads/mpich-4.2.1/src/mpl/include -I/home/rafay/Downloads/mpich-4.2.1/modules/json-c -D_REENTRANT -I/home/rafay/Downloads/mpich-4.2.1/src/mpi/romio/include -I/home/rafay/Downloads/mpich-4.2.1/src/pmi/include -I/home/rafay/Downloads/mpich-4.2.1/modules/yaksa/src/frontend/include -I/home/rafay/Downloads/mpich-4.2.1/modules/libfabric/include'
    Process Manager:                         pmi
    Launchers available:                     ssh rsh fork slurm ll lsf sge manual persist
    Topology libraries available:            hwloc
    Resource management kernels available:   user slurm ll lsf sge pbs cobalt
    Demux engines available:                 poll select

My program: hello.py

from mpi4py import MPI
MPI = MPI.COMM_WORLD
size = comm.size
rank = comm.rank

print(f"{rank} of {size}")

The output that I get after I run: mpirun -np 4 python hello.py or mpiexec -n 4 python hello.py is the following message repeated 8 times

hwloc/linux: Ignoring PCI device with non-16bit domain.
Pass --enable-32bits-pci-domain to configure to support such devices
(warning: it would break the library ABI, don't enable unless really needed).

with

hello 0 of 1
hello 0 of 1
hello 0 of 1
hello 0 of 1

The output should show processors, and each rank. But it clearly shows that MPI isn’t running properly.

I have dualboot system, so I ran the same program on my Windows, and it worked fine there. So I am not sure what the problem is. My doubts are that I may have installed MPICH incorrectly? (So I might have to reinstall that?), but I am clueless if that really is the case. Any help would be appreciated, thank you!