Python

Debugger: debugpy (Microsoft) Status: Stable Python version: 3.8+

Prerequisites

pip install debugpy

Verify: python -m debugpy --version

Quick Start

# Debug a script
krometrail launch "python app.py" --break app.py:42

# Debug a pytest test
krometrail launch "python -m pytest tests/test_order.py::test_gold_discount -x" \
	--break order.py:147

# Debug Django
krometrail launch "python manage.py runserver" --break views.py:83

# Debug Flask
krometrail launch "flask run" --break routes.py:55

Framework Auto-detection

pytest, Django, and Flask are auto-detected from the launch command. The adapter configures debugpy appropriately for each:

• pytest — disables test runner capture so breakpoints work correctly
• Django — enables Django template debugging, disables autoreload
• Flask — sets WERKZEUG_RUN_MAIN=true to prevent fork on autoreload

Conditional Breakpoints

Python expressions work directly in conditions:

krometrail break "order.py:147 when discount < 0"
krometrail break "loop.py:25 when i == 99"
krometrail break "api.py:30 when request.method == 'POST'"

Exception Breakpoints

krometrail break --exceptions uncaught    # only unhandled exceptions
krometrail break --exceptions raised      # all raised exceptions

For specific exception types, use a conditional breakpoint with isinstance.

Tips

• The Python adapter uses python -m debugpy --listen :PORT --wait-for-client under the hood. You do not need to modify your code.
• debug_evaluate accepts any valid Python expression including method calls, comprehensions, and f-strings.
• Virtual environments are respected — the adapter uses the python found in your PATH or the one specified in the command.
• Use --stop-on-entry to pause on the first executable line (useful for understanding program structure).

Troubleshooting

Breakpoints not hit:

• Confirm the file path is correct relative to cwd
• Check that krometrail doctor shows debugpy installed
• If using a virtual environment, ensure it's activated before launching

debugpy import error in your program:

• debugpy is only used by Krometrail's adapter subprocess, not imported into your code directly