No module named 'pycmsg'

[MartianColonist]

After installing MSG-1.3 on Ubuntu 20.04 in a fresh conda environment, I'm hitting the following error upon importing pymsg:

Traceback (most recent call last):
import pymsg as pymsg
File "/home/....../anaconda3/envs/....../lib/python3.11/site-packages/pymsg/init.py", line 29, in
import pycmsg as pyc
ModuleNotFoundError: No module named 'pycmsg'

Is there any additional step, beyond those in the installation instructions in the MSG documentation, to install the pycmsg submodule?

[MartianColonist]

It looks like to solve this problem the user needs 'cython' to be installed in their conda environment before compiling MSG ('make -j -C $MSG_DIR').

Can you add a note on the installation page under 'Building MSG' noting that cython is a prerequisite for pymsg?

[rhdtownsend]

Nice catch. I though I had set things up so that when Cython isn't available, the generated C source code (src/cython/pycmsg.c) gets used instead. However, the vpath definitions necessary to make this work are missing from build/Make.inc.

As a workaround, if you don't want to install Cython, just run the following before you run make:

cp $MSG_DIR/src/cython/pycmsg.c $MSG_DIR/build/