appendix-d
Appendix D. Troubleshooting Common Errors
When an example does not work, the cause is usually one of a small number of recurring issues: a key that is not set, a package that is not installed, an API that changed, or data that is shaped differently than the code expects. This appendix groups the errors you are most likely to hit by category, with the symptom, the usual cause, and the fix. Where a full setup is involved, it points you to Appendix A.
D.1 Environment and setup
Table D.1 Environment errors
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Symptom
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Cause
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Fix
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command not found: python
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Python isn't installed, or your system only exposes it as python3
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First confirm Python 3.8+ is actually installed (Appendix A); if it is, the command is usually python3 and pip3 (Mac/Linux). Confirm your virtual environment is active (prompt shows (venv))
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ModuleNotFoundError: No module named 'X'
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Package not installed, or the wrong Python is active
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Activate the venv, then
pip install -r requirements.txt. Confirm with
pip list
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Jupyter can't find an installed package
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Jupyter is running a different Python than your venv
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Install Jupyter inside the venv and register a kernel:
python -m ipykernel install --user --name=venv, then pick that kernel
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pip install fails or is slow
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Old pip, wrong Python version, or a slow network connection
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pip install --upgrade pip; confirm Python 3.8+
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