ImportError: No module named mpi4py

Question

I am brand new to parallel computing and I'm trying to set up a small cluster of Raspberry Pi's to fiddle around with. Whenever I went to install mpi4py, I used pip3 install mpi4py but I am still getting the following error when I try to run a simple test script. I am able to use mpiexec with a Hello World script that prints "Hello" for every core in the cluster.

Hardware is a cluster Raspberry Pi 3B+ running Rasbian Lite

test.py:

from mpi4py import MPI

print("Test")

This is the readout that I am getting from the command line:

Traceback (most recent call last):
  File "test.py", line 1, in <module>
    from mpi4py import MPI
ImportError: No module named mpi4py

Thanks in advance

How are you running the script? Is it with the version of python that reads from the library that pip3 installs to? — chepner
– chepner, Commented Apr 22, 2022 at 16:37
I always use python -m pip install to make sure packages end up in the right python installation. — Open AI - Opting Out
– Open AI - Opting Out, Commented Apr 22, 2022 at 16:37
Does this answer your question? Python beginner - No module named 'mpi4py' — Thavas Antonio
– Thavas Antonio, Commented Apr 22, 2022 at 16:39
@chepner I am running the script with mpiexec -hostlist nodes_ips python test.py When I try to run python -m pip install mpi4py, I am getting an error that there is not module named 'pip' — Sacooley1
– Sacooley1, Commented Apr 22, 2022 at 17:01

Sacooley1 · Accepted Answer · 2022-04-23 22:16:21Z

1

I found the solution, and frankly I feel a little silly now. I wasn't aware that Debian for Raspberry Pi comes preinstalled with both Python 2 and Python 3, so I have run to mpiexec -hostlist nodes_ips python3 test.py instead.

answered Apr 23, 2022 at 22:16

Sacooley1

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1 Comment

antont Over a year ago

Maybe it's Python and distros which are a bit silly here. But yes you used pip3 explicitly so that goes with explicit python3. Luckily the painful 2-> 3 transition is I guess pretty much done finally now, and maybe some time before year 3000 there's only 3 and that also as default everywhere (py 3 project was called Python 3000 initially).

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