Question: I am using Poetry to manage a Python project. I create a virtual environment for Poetry using a normal poetry install and pyproject.toml workflow. Visual Studio Code and its PyLance does not pick up project dependencies in Jupyter Notebook.  Python stdlib modules are recognised The modules of my application are recognised The modules in the dependencies and libraries my application uses are not recognised  Instead, you get an error Import "xxx" could not be resolved Pylance (reportMissingImports)  An example screenshot with some random imports that show what is recognised and what is not (tradeexecutor package is Poetry project, then some random Python packages dependency are not recognised).:   The notebook still runs fine within Visual Studio Code, so the problem is specific to PyLance, the virtual environment is definitely correctly set up. Some Python Language Server output (if relevant): 2024-03-01 10:15:40.628 [info] [Info - 10:15:40] (28928) Starting service instance "trade-executor" 2024-03-01 10:15:40.656 [info] [Info - 10:15:40] (28928) Setting pythonPath for service "trade-executor": "/Users/moo/code/ts/trade-executor" 2024-03-01 10:15:40.657 [info] [Info - 10:15:40] (28928) Setting environmentName for service "trade-executor": "3.10.13 (trade-executor-8Oz1GdY1-py3.10 venv)" 2024-03-01 10:15:40.657 [info] [Info - 10:15:40] (28928) Loading pyproject.toml file at /Users/moo/code/ts/trade-executor/pyproject.toml 2024-03-01 10:15:40.657 [info] [Info - 10:15:40] (28928) Pyproject file "/Users/moo/code/ts/trade-executor/pyproject.toml" has no "[tool.pyright]" section. 2024-03-01 10:15:41.064 [info] [Info - 10:15:41] (28928) Found 763 source files 2024-03-01 10:15:41.158 [info] [Info - 10:15:41] (28928) Background analysis(4) root directory: file:///Users/moo/.vscode/extensions/ms-python.vscode-pylance-2024.2.2/dist 2024-03-01 10:15:41.158 [info] [Info - 10:15:41] (28928) Background analysis(4) started 2024-03-01 10:15:41.411 [info] [Info - 10:15:41] (28928) Indexer background runner(5) root directory: file:///Users/moo/.vscode/extensions/ms-python.vscode-pylance-2024.2.2/dist (index) 2024-03-01 10:15:41.411 [info] [Info - 10:15:41] (28928) Indexing(5) started 2024-03-01 10:15:41.662 [info] [Info - 10:15:41] (28928) scanned(5) 1 files over 1 exec env 2024-03-01 10:15:42.326 [info] [Info - 10:15:42] (28928) indexed(5) 1 files over 1 exec  Also looks like PyLance correctly finds the virtual environment in the earlier Python Language Server output: 2024-03-03 19:36:56.784 [info] [Info - 19:36:56] (41658) Pylance language server 2024.2.2 (pyright version 1.1.348, commit cfb1de0c) starting 2024-03-03 19:36:56.789 [info] [Info - 19:36:56] (41658) Server root directory: file:///Users/moo/.vscode/extensions/ms-python.vscode-pylance-2024.2.2/dist 2024-03-03 19:36:56.789 [info] [Info - 19:36:56] (41658) Starting service instance "trade-executor" 2024-03-03 19:36:57.091 [info] [Info - 19:36:57] (41658) Setting pythonPath for service "trade-executor": "/Users/moo/Library/Caches/pypoetry/virtualenvs/trade-executor-8Oz1GdY1-py3.10/bin/python" 2024-03-03 19:36:57.093 [info] [Info - 19:36:57] (41658) Setting environmentName for service "trade-executor": "3.10.13 (trade-executor-8Oz1GdY1-py3.10 venv)" 2024-03-03 19:36:57.096 [info] [Info - 19:36:57] (41658) Loading pyproject.toml file at /Users/moo/code/ts/trade-executor/pyproject.toml  How to diagnose the issue further and then fix the issue?

Answer: Some other people were having the same issue.  Pylance does not show auto import information from site-packages directory #3281 Pylance not indexing all files and symbols for sqlalchemy even with package depth of 4  Visual Studio Code's PyLance implementation seems to have some internal limits that may prevent indexing all files. However, this was not the case for me. Instead, PyLance was somehow corrupted. Running: PyLance: Clear all persistent indices from the command palette fixed the issue for. After this, PyLance seemed to behave.