How to use --pdbcls parameter to attach to VSCode Debugger

[programmerPhysicist]

I've tried the following command: pytest --pdbcls=debugpy:launcher, so that pytest will attach to the debugpy debugger, which is used in a VSCode python extension to debug python code. Nothing seems to happen. Anybody know the correct way to do it, so that it will attach to the debugger in VSCode?

[portyu9]

Hi @programmerPhysicist

--pdbcls is not intended to specify a VS Code/debugpy launcher.

This option:

--pdbcls=module:class

expects a class implementing the pdb.Pdb-style debugger interface.

So:

pytest --pdbcls=debugpy:launcher

doesn't attach pytest to VS Code because debugpy.launcher is not a pdb.Pdb implementation.

For VS Code/debugpy, start pytest under debugpy instead:

python -m debugpy --listen 5678 --wait-for-client -m pytest

or for a particular test:

python -m debugpy \
    --listen 5678 \
    --wait-for-client \
    -m pytest tests/test_example.py::test_example

Then attach VS Code to:

localhost:5678

with a Python attach configuration.

Once VS Code is attached, regular breakpoints in your test/application code can be used normally.

You can also explicitly stop in the debugger with:

import debugpy

debugpy.breakpoint()

if appropriate.

The distinction is:

pytest --pdb / --pdbcls
        ↓
Python PDB-compatible interactive debugger

debugpy
        ↓
Debug Adapter Protocol server used by VS Code

They solve different problems.

If your goal is simply to debug a pytest test from VS Code, VS Code's Python testing integration can also launch the selected pytest test under its debugger directly, which avoids manually using --pdbcls.

Please mark this answer as accepted if it helped, thank you.