Python Environments, Pylance, pytest, and debugpy

For extension choices and batch installation scope, see language extensions and Profiles.

This guide uses a separate Python development/test project. Its width and file layout differ from the Ruff formatting lab; choose the configuration for the project you are opening.

Separate extension responsibilities

Compare existing Black/isort/Flake8 behavior before migrating a real team. Ruff does not replace type checking or tests. Python environments, Ruff extension

Match the selected interpreter to execution

In an empty directory, prepare uv using its installation guide and run:

uv init --name vscode-python-lab --python 3.12
uv add --dev ruff pytest pyright
uv sync --locked
uv run python -c "import sys; print(sys.executable); print(sys.version)"

Commit pyproject.toml, .python-version, and uv.lock; exclude .venv. Retain an existing Poetry, Conda, or pip-tools workflow in other projects. uv projects

Use Python: Select Interpreter to select .venv. Open a fresh terminal and compare python -c "import sys; print(sys.executable)" with uv's output. Windows uses .venv/Scripts/python.exe; POSIX uses .venv/bin/python. Notebooks require a separate kernel check. Kernel management

Configure format, imports, types, and tests

Merge into pyproject.toml, preserving generated project/dependency sections:

[tool.ruff]
target-version = "py312"
line-length = 88

[tool.ruff.lint]
select = ["E4", "E7", "E9", "F", "I"]

[tool.ruff.format]
quote-style = "double"
indent-style = "space"

[tool.pyright]
typeCheckingMode = "standard"
include = ["main.py", "tests"]
venvPath = "."
venv = ".venv"

[tool.pytest.ini_options]
testpaths = ["tests"]

I rules organize imports. Apply lint fixes before formatting; do not enable competing layout lint rules. Align width with your text policy. Pylance and CLI Pyright can differ by release, so compare diagnostic codes and versions when necessary. Ruff formatting, Pyright configuration

Merge settings.json:

{
    "python.testing.pytestEnabled": true,
    "python.testing.unittestEnabled": false,
    "python.testing.pytestArgs": ["tests"],
    "python.analysis.autoImportCompletions": true,
    "ruff.importStrategy": "fromEnvironment",
    "[python]": {
        "editor.defaultFormatter": "charliermarsh.ruff",
        "editor.formatOnSave": true,
        "editor.formatOnPaste": false,
        "editor.formatOnType": false,
        "editor.codeActionsOnSave": {
            "source.fixAll": "never",
            "source.organizeImports": "never",
            "source.fixAll.ruff": "explicit",
            "source.organizeImports.ruff": "explicit"
        }
    }
}

Keep Pylance diagnostics. Do not hide all type analysis to remove overlapping warnings. Ruff's fromEnvironment strategy can fall back to a bundled executable; inspect Output and compare uv run ruff --version. Avoid legacy python.formatting.provider, python.linting.*, or python.pythonPath examples. Ruff editor settings, Python formatting

Add a runnable test

Create main.py:

def total(price: int, quantity: int) -> int:
    return price * quantity


if __name__ == "__main__":
    print(total(1200, 3))

Create tests/test_main.py:

from main import total


def test_total() -> None:
    assert total(1200, 3) == 3600

Run:

uv run python -m pytest
uv run ruff check .
uv run ruff format --check .
uv run pyright

Discover and debug test_total in Testing with a breakpoint in total. If discovery fails, inspect Python Test Log and uv run python -m pytest --collect-only. Apply Ruff fixes, then format, review, and rerun all checks. Python testing

Launch with debugpy

Create launch.json:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: project main",
            "type": "debugpy",
            "request": "launch",
            "program": "${workspaceFolder}/main.py",
            "cwd": "${workspaceFolder}",
            "console": "integratedTerminal",
            "justMyCode": true
        },
        {
            "name": "Python: pytest",
            "type": "debugpy",
            "request": "launch",
            "module": "pytest",
            "args": ["tests", "-q"],
            "cwd": "${workspaceFolder}",
            "console": "integratedTerminal",
            "justMyCode": true
        }
    ]
}

Use module mode for package entry points when appropriate. Without an explicit Python override, launch uses the selected interpreter. Set justMyCode false only when investigating dependencies. Python debugging

For FastAPI/Django reloaders, identify the actual child process; start with reload disabled to narrow a reproduction. Check an actual request rather than only successful startup.

Diagnose differences

Try navigation, Rename, and Extract on a small tested function first. Dynamic attributes and decorators need additional review. Fix package installation and source layout before adding arbitrary extraPaths. Python editing

Use the official Python getting-started video for the environment and debugging flow, and this guide for Ruff settings.