`PYTHONPATH` from shell no longer respected after latest update

[ironhak]

Description

After updating to the latest version of ipykernel, the environment variable PYTHONPATH set in my shell is no longer reflected inside Jupyter notebooks.

Previously, I could import my own local modules directly, e.g.:

from my_module import my_function

where my_module.py is located in a custom folder appended to PYTHONPATH in my .bashrc:

export PYTHONPATH="$PYTHONPATH:/path/to/custom/library"

After the update, notebooks in vscode no longer find these modules unless I manually add the path within the notebook using:

import sys
sys.path.append("/path/to/custom/library")

Expected behavior

Jupyter kernels should inherit the PYTHONPATH from the parent shell (as they did prior to the update).

Actual behavior

PYTHONPATH is ignored; sys.path inside the kernel does not contain my custom directory.