callback added by `doc.on_session_destroyed()` cannot access module level imports / variables

[orionlee]

Software versions

Python version        :  3.11.10 | packaged by conda-forge | (main, Sep 22 2024, 14:10:38) [GCC 13.3.0]
IPython version       :  9.3.0
Tornado version       :  6.5.1
NumPy version         :  1.26.4
Bokeh version         :  3.7.3
BokehJS static path   :  /.../lib/python3.11/site-packages/bokeh/server/static
node.js version       :  (not installed)
npm version           :  (not installed)
jupyter_bokeh version :  (not installed)
Operating system      :  Linux-6.6.87.2-microsoft-standard-WSL2-x86_64-with-glibc2.31

Browser name and version

Chrome 137

Jupyter notebook / Jupyter Lab version

N/A

Expected behavior

Discussed at: https://discourse.bokeh.org/t/on-session-destroyed-cannot-access-module-level-imports-variables/12482

For a on_session_destroyed callback is added via doc.on_session_destroyed(), it should have access to module level imports / variables like typical functions.

Observed behavior

The callback appears to run in some isolated context, and does not have access to to module level imports / variables.

Example code

Run the following codes with `bokeh serve` (either as a 1-file app or a directory app). Bokeh server would report an error in running the callback, complaining that the module level import `np` is not defined.

DocumentLifeCycleHandler on_session_destroyed callback <function my_on_session_destroyed at 0x714ea77614e0>  failed with following error: name 'np' is not defined


The example codes:

from bokeh.io import curdoc
from bokeh.layouts import layout
from bokeh.plotting import figure, ColumnDataSource

import numpy as np


def my_on_session_destroyed(session_context):
    # # Uncomment the following line to make the codes to work
    # #  (the module level import seems to have no effect here)
    # import numpy as np
    print("my_on_session_destroyed():", np.nan)


def create_interact_ui(doc):
    fig = figure(
        title="Test Bokeh server",
    )

    source = ColumnDataSource(data=dict(
        x=np.array([0, 5, 10], dtype=float),
        y=np.array([4, 6, 8], dtype=float),
        ))
    fig.scatter(source=source, size=16, marker="square", fill_color="red")

    doc.add_root(layout([
        [fig, ]
    ]))
    doc.on_session_destroyed(my_on_session_destroyed)


#
# Main
#
create_interact_ui(curdoc())

Stack traceback or browser console output

No response

Screenshots

No response