fix: use math.ceil() instead of int() for n_local_cores to prevent ZeroDivisionError on single-core machines

[Mani212005]

Describe your changes

When using --dask-distributed-local-core-fraction with a value between 0 and 1 on a
single-core machine (e.g. standard GitHub CI), the following line:

n_local_cores = int(args.dask_distributed_local_core_fraction * n_system_cores)

truncates towards zero. For example:

int(0.5 * 1) = 0

This causes a ZeroDivisionError when computing memory_per_worker:

memory_per_worker = total_memory / n_local_cores * args.dask_distributed_local_memory_fraction
#                                  ^^^^^^^^^^^^^ ZeroDivisionError when n_local_cores == 0

The fix replaces int() with math.ceil() to always round up to at least 1 worker:

n_local_cores = math.ceil(args.dask_distributed_local_core_fraction * n_system_cores)

This ensures n_local_cores >= 1 regardless of the fraction or number of system cores.

Changes:

• cli.py — Added import math and replaced int() with math.ceil() for the n_local_cores calculation.
• test_distributed.py — Added "0.5" as a parametrized test case to cover the fractional value scenario that triggered the bug.

Testing — all 4 distributed tests pass:

tests/test_distributed.py::test_run_distributed[args0]  PASSED  (core-fraction=1.0)
tests/test_distributed.py::test_run_distributed[args1]  PASSED  (core-fraction=0.5) ← new
tests/test_distributed.py::test_run_distributed[args2]  PASSED  (core-fraction=0.0)
tests/test_distributed.py::test_run_distributed[args3]  PASSED  (no dask args)

4 passed in 150.24s

Issue Link

Closes #32

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation (Addition or improvements to documentation)

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[joeloskarsson]

Hi! Could you reformat this PR using our existing PR template: https://github.com/mllam/mllam-data-prep/blob/main/.github/pull_request_template.md ? This guarantees that we follow the development workflows that we have in place. If you have questions about some parts of it feel free to ask!

[Mani212005]

@joeloskarsson
Sorry for that! I have corrected the format kindly review the code.
Thank you !

[joeloskarsson]

How did this test pass if --dask-distributed-local-core-fraction 0.0 results in division by zero? Seems to potentially point to an issue with the test that should then be fixed here as well.

[Mani212005]

Hello @joeloskarsson, I believe the reason the test passes is due to

args.dask_distributed_local_core_fraction > 0.0:

in the cli.py at 54th line file as when 0.0 is provided the above condition becomes False so the entire
dask block is skipped thus the test passes. But you are right I should have been more clear I will add comments for better clarity.
Thank you!