Output under MPI

If I try to use rich output under MPI, I get blank lines. Here’s an example:

# test.py
from mpi4py import MPI
rank = MPI.COMM_WORLD.Get_rank()

from rich import print
print(rank)

mpirun -n 2 python3 test.py

Produces four blank lines.

Even if I wrap the output to only run on rank 0, i.e.,

if rank == 0:
    from rich import print
    print(rank)

I still get only blank lines (this time two of them).

What’s causing this, and how can I fix it?

[mrzv]

Ah, great. Thanks for figuring it out. I think this qualifies as a bug I should report upstream to OpenMPI. And the workaround is great, too.

[willmcgugan]

I’ve figure out what is going on. When run with MPI, the shutil.get_terminal_size function reports a terminal size of (0, 0). Rich wraps text to the column width, and when you wrap to a width of 0 all you are left with is blank lines.

I think this must be a bug in how MPI sets the environment for processes.

A workaround would be to define a COLUMNS environment var with your desired terminal width. Or construct Console with an explicit width.

console = Console(width=80)
console.print(rank) # This works!