Cannot find context for 'forkserver' on Windows VS Code

[linwe2012]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Buckaroo.

What type of jupyter notebook were you using (VSCode notebook, google colab, Jupyter Lab, Jupyter notebook). Select multiple if you can reproduce this in multiple environments. If other, please add to description.

VS Code

Reproducible example

import buckaroo

Issue description

Vscode jupyter notebook cannot import buckaroo with cannot find context for 'forkserver' error

Expected behavior

.

Installed versions

0.12.4

Jupyter Log output

[paddymul]

Thanks for trying buckaroo. What platform are you running on? OS X? Linux? Windows?

Can you try
buckaroo.debug_packages() and paste the output here?

[paddymul]

oops, I just saw windows in the title.

Yep, I thought the new execution framework might have trouble with windows. let me try some things.

[paddymul]

I think the fix will be pretty simple, just a conditional import if windows. For now, can you try running buckaroo in an environment without polars, which should work.

I guess it's time for windows CI too

[paddymul]

I think this is fixed in CI when I have run against windows.

To test please create a new python environment on windows, the following commands should reproduce

uv venv --python 3.11  # creates a .venv in the current directory
uv pip install polars
uv pip install buckaroo
python -c "import buckaroo"
python -c "from buckaroo import read" # expect this to fail
uv pip install jupyterlab
jupyterlab

if that works try importing buckaroo in a jupyter notebook.

read and read_df shouldn't be available to windows users. importing those commands causes the failures, and there is now a guard statement around it. https://github.com/buckaroo-data/buckaroo/blob/main/buckaroo/__init__.py#L119-L129

[linwe2012]

Thanks for support, @paddymul! However, I upgraded my package to 0.12.5 and the issue persists. Should I wait for the next release?

[ijstokes]

Tried to reproduce this. Instead of

uv pip install buckaroo

I did the following:

git clone https://github.com/buckaroo-data/buckaroo.git
cd buckaroo
source .venv/Scripts/activate
uv pip install build
python -m build
uv pip install ./dist/buckaroo-0.12.5-py3-none-any.whl

And that went fine. I built the package from the head of main a few minutes ago, from c7d6ec5

Then I proceeded with the next step, which is when I got errors:

python -c "import buckaroo"

resulted in:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\buckaroo\__init__.py", line 5, in <module>
    from .buckaroo_widget import BuckarooWidget, BuckarooInfiniteWidget, AutocleaningBuckaroo
  File "C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\buckaroo\buckaroo_widget.py", line 77, in <module>
    class BuckarooWidgetBase(anywidget.AnyWidget):
  File "C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\traitlets\traitlets.py", line 963, in __new__
    return super().__new__(mcls, name, bases, classdict, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\anywidget\widget.py", line 71, in __init_subclass__
    file_contents = try_file_contents(getattr(cls, key))
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\anywidget\_util.py", line 280, in try_file_contents
    raise FileNotFoundError(msg)
FileNotFoundError: File not found: C:\Users\ianst\othercode\buckaroo\.venv\Lib\site-packages\buckaroo\static\compiled.css

So I never got to the import which was supposed to cause an error:

python -c "from buckaroo import read" # expect this to fail

[ijstokes]

If I go straight from a network pip install, and execute almost the exact sequence above, but with a source .venv/Scripts/activate after the first line, then I still get a stack trace at the import buckaroo command, but with a different error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\ianst\othercode\test-buckaroo\.venv\Lib\site-packages\buckaroo\__init__.py", line 9, in <module>
    from .file_cache.cache_utils import (
  File "C:\Users\ianst\othercode\test-buckaroo\.venv\Lib\site-packages\buckaroo\file_cache\__init__.py", line 7, in <module>
    from .mp_calibration import (
  File "C:\Users\ianst\othercode\test-buckaroo\.venv\Lib\site-packages\buckaroo\file_cache\mp_calibration.py", line 14, in <module>
    from .mp_timeout_decorator import mp_timeout
  File "C:\Users\ianst\othercode\test-buckaroo\.venv\Lib\site-packages\buckaroo\file_cache\mp_timeout_decorator.py", line 145, in <module>
    ctx = multiprocessing.get_context("forkserver")
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\ianst\AppData\Roaming\uv\python\cpython-3.11.14-windows-x86_64-none\Lib\multiprocessing\context.py", line 243, in get_context
    return super().get_context(method)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\ianst\AppData\Roaming\uv\python\cpython-3.11.14-windows-x86_64-none\Lib\multiprocessing\context.py", line 193, in get_context
    raise ValueError('cannot find context for %r' % method) from None
ValueError: cannot find context for 'forkserver'

I should note that this is running on a win-64 system:

Edition	Windows 11 Pro
Version	25H2
Installed on	‎8/‎12/‎2025
OS build	26200.7623
Experience	Windows Feature Experience Pack 1000.26100.275.0

Device name	rouge
Processor	Intel(R) N100 (800 MHz)
Installed RAM	16.0 GB (15.7 GB usable)
Device ID	1A7CBCE4-DF85-4936-9765-4319D0A35260
Product ID	00330-50000-00000-AAOEM
System type	64-bit operating system, x64-based processor
Pen and touch	No pen or touch input is available for this display

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