openEMS.pyx AssertionError due to checking non-canonical path name

[biergaizi]

Currently, running openEMS's example Python scripts on macOS always fails with the following error:

$ python3 MSL_NotchFilter.py 
Traceback (most recent call last):
  File "/Users/gentoo/code/openEMS-Project/openEMS/python/Tutorials/MSL_NotchFilter.py", line 103, in <module>
    FDTD.Run(Sim_Path, cleanup=True)
  File "openEMS/openEMS.pyx", line 489, in openEMS.openEMS.openEMS.Run
AssertionError

This is caused by an oversight of an assertion in openEMS.pyx:

os.chdir(sim_path)
# ...
assert os.getcwd() == sim_path

The problem here is that sim_path is not a canonical path name, so the assertion would fail if the path we're switching into contains a symbolic link. This problem affects all operating systems, it's not limited to macOS. But on macOS, the problem is especially serious, since macOS's /tmp is a link to /private/tmp by default. Thus, it causes an AssertionError in all the included Python examples.

$ python3
Python 3.11.3 (main, May  3 2023, 02:26:34) [GCC 12.2.0] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.realpath("/tmp")
'/private/tmp'
>>> os.chdir("/tmp")
>>> os.getcwd()
'/private/tmp'

Instead of doing assert os.getcwd() == sim_path, we should do assert os.getcwd() == os.path.realpath(sim_path) instead. I'll submit my patch in a Pull Request to fix this problem.

[biergaizi]

I just opened Pull Request #114 to fix this problem. It has been successfully tested on macOS.

[thliebig]

Running with "python -O" should avoid this with the unpatched version as it ignores asserts