Ubuntu-Specific Errors

These errors are specific to running MOSAIC on Ubuntu (native Linux). For shared errors that apply to both platforms, see the parent Common Errors page.

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box2d-py – “ModuleNotFoundError: No module named ‘swig’”

Error (when installing box2d environments):

Building wheel for box2d-py (pyproject.toml) did not run successfully.
swigging Box2D/Box2D.i to Box2D/Box2D_wrap.cpp
swig -python -c++ -IBox2D -small -O -includeall -ignoremissing -w201 ...
Traceback (most recent call last):
  File "/home/hamid/.local/bin/swig", line 5, in <module>
    from swig import swig
ModuleNotFoundError: No module named 'swig'
error: command '/home/hamid/.local/bin/swig' failed with exit code 1

Cause: A broken SWIG Python script exists at ~/.local/bin/swig that tries to import a non-existent Python module called swig. This script shadows the proper system SWIG binary at /usr/bin/swig.

The box2d-py package requires SWIG (Simplified Wrapper and Interface Generator) to build its C++ extensions. When pip tries to build the wheel, it finds the broken script first because ~/.local/bin appears earlier in PATH than /usr/bin.

Fix:

# Remove or rename the broken SWIG script
mv ~/.local/bin/swig ~/.local/bin/swig.broken

# Verify system SWIG is now being used
which swig    # Should show /usr/bin/swig or /bin/swig
swig -version # Should show SWIG Version 4.x

# Retry the installation
pip install -e ".[box2d]"

If system SWIG is not installed, install it first:

sudo apt-get install -y swig

Note

This issue occurs when a Python package (possibly installed via pip) created a wrapper script at ~/.local/bin/swig instead of using the system SWIG. The wrapper script is non-functional and must be removed to allow the proper SWIG binary to be used.