I’ve opened a project with the following structure in VS Code (1.71.0 on macOS, Intel) and activated a Dev Container (I’ve tried the default Python 3.9 and 3.10 containers from Microsoft, with and without using python3 -m venv ...):

project/
  .devcontainer/
    devcontainer.json
    Dockerfile
  foo/
    foo/
      tests/
        test_bar.py  <-- IDE reports import error in this file
      resources/
      __init__.py
      bar.py
    setup.py

In VS Code’s terminal window, I can successfully run test_bar.py from directory project/foo with:

python3 -m unittest discover foo/tests -p 'test_*.py'

So the project is valid and runs OK from the command line.

But when I open file project/foo/foo/tests/test_bar.py in VS Code, I see the error Unable to import 'foo' pylint(import-error) underlined in red for the following line:

from foo import bar

I see similar supposed errors for external packages I’ve installed with pip3 install.

I’ve tried to inform VS Code by adding various relative and absolute paths (e.g. /workspaces/project/foo) to various places in project/.devcontainer.json, such as at:

• customizations.vscode.settings
  • python.analysis.extraPaths
  • python.autoComplete.extraPaths
  • python.testing.unittestargs

But I’ve had no luck so far (after many IDE restarts and container image rebuilds).

So I’m left wondering; how should one fix such IDE-flagged import errors in VS Code when using a Dev Container?

Additional Info

As a file was requested in the comments, here are the key test project files I used (I’ve not fixed any paths; my last test project was named vscode-python-dev-container, not project, which I used as shorthand above).

devcontainer.json (with the containerEnv section added for the suggested PYTHONPATH change):

// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
// https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/python-3
{
    "name": "Python 3",
    "build": {
        "dockerfile": "Dockerfile",
        "context": "..",
        "args": { 
            // Update 'VARIANT' to pick a Python version: 3, 3.10, 3.9, 3.8, 3.7, 3.6
            // Append -bullseye or -buster to pin to an OS version.
            // Use -bullseye variants on local on arm64/Apple Silicon.
            "VARIANT": "3.10-bullseye",
            // Options
            "NODE_VERSION": "lts/*"
        }
    },

    "containerEnv": {
        "PYTHONPATH": "/workspaces/vscode-python-dev-container/foo"
    },

    // Configure tool-specific properties.
    "customizations": {
        // Configure properties specific to VS Code.
        "vscode": {
            // Set *default* container specific settings.json values on container create.
            "settings": { 
                "python.defaultInterpreterPath": "/usr/local/bin/python",
                "python.linting.enabled": true,
                "python.linting.pylintEnabled": true,
                "python.formatting.autopep8Path": "/usr/local/py-utils/bin/autopep8",
                "python.formatting.blackPath": "/usr/local/py-utils/bin/black",
                "python.formatting.yapfPath": "/usr/local/py-utils/bin/yapf",
                "python.linting.banditPath": "/usr/local/py-utils/bin/bandit",
                "python.linting.flake8Path": "/usr/local/py-utils/bin/flake8",
                "python.linting.mypyPath": "/usr/local/py-utils/bin/mypy",
                "python.linting.pycodestylePath": "/usr/local/py-utils/bin/pycodestyle",
                "python.linting.pydocstylePath": "/usr/local/py-utils/bin/pydocstyle",
                "python.linting.pylintPath": "/usr/local/py-utils/bin/pylint"
            },
            
            // Add the IDs of extensions you want installed when the container is created.
            "extensions": [
                "ms-python.python",
                "ms-python.vscode-pylance"
            ]
        }
    },

    // Use 'forwardPorts' to make a list of ports inside the container available locally.
    // "forwardPorts": [],

    // Use 'postCreateCommand' to run commands after the container is created.
    // "postCreateCommand": "pip3 install --user -r requirements.txt",

    // Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
    "remoteUser": "vscode"
}

Dockerfile:

# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/python-3/.devcontainer/base.Dockerfile

# [Choice] Python version (use -bullseye variants on local arm64/Apple Silicon): 3, 3.10, 3.9, 3.8, 3.7, 3.6, 3-bullseye, 3.10-bullseye, 3.9-bullseye, 3.8-bullseye, 3.7-bullseye, 3.6-bullseye, 3-buster, 3.10-buster, 3.9-buster, 3.8-buster, 3.7-buster, 3.6-buster
ARG VARIANT="3.10-bullseye"
FROM mcr.microsoft.com/vscode/devcontainers/python:0-${VARIANT}

# [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
ARG NODE_VERSION="none"
RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi

# [Optional] If your pip requirements rarely change, uncomment this section to add them to the image.
# COPY requirements.txt /tmp/pip-tmp/
# RUN pip3 --disable-pip-version-check --no-cache-dir install -r /tmp/pip-tmp/requirements.txt 
#    && rm -rf /tmp/pip-tmp

# [Optional] Uncomment this section to install additional OS packages.
# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive 
#     && apt-get -y install --no-install-recommends <your-package-list-here>

# [Optional] Uncomment this line to install global node packages.
# RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1

bar.py:

"""An example module."""
JSON_STR = '{"a": 1}'

test_bar.py:

"""An example test."""
import json
import unittest
import requests  # test external lib access
from foo import bar

class TestFooBar(unittest.TestCase):
    """An example test class."""
    a = requests.__name__  # to eliminate warning above that package isn't used
    def test_foo_bar_json(self):
        """An example test."""
        data = json.loads(bar.JSON_STR)
        self.assertEqual(data['a'], 1)