Apply suggestions from code review #293

Job	Run time
lint (mypy)	2m 54s
lint (black)	18s
lint (flake8)	19s
lint (pydocstyle)	0s
Test API, headers and no-engine mode	3m 39s
test-clean-install-ubuntu	1m 18s
test-clean-install-windows	3m 8s
test cloud	4m 36s
Test BaseOnPython execution, Python 3.8	18m 3s
test-ubuntu (engine python, python 3.8, group_1)	3m 46s
test-ubuntu (engine ray, python 3.8, group_1)	3m 58s
test-ubuntu (engine ray, python 3.8, group_2)	3m 44s
test-ubuntu (engine ray, python 3.8, group_3)	3m 57s
test-ubuntu (engine ray, python 3.8, group_4)	3m 52s
test-ubuntu (engine dask, python 3.8, group_1)	3m 51s
test-ubuntu (engine dask, python 3.8, group_2)	3m 58s
test-ubuntu (engine dask, python 3.8, group_3)	3m 45s
test-ubuntu (engine dask, python 3.8, group_4)	3m 40s
test-windows (engine python, python 3.8, group_1)	3m 43s
test-windows (engine ray, python 3.8, group_1)	3m 43s
test-windows (engine ray, python 3.8, group_2)	3m 43s
test-windows (engine ray, python 3.8, group_3)	24s
test-windows (engine ray, python 3.8, group_4)	2m 21s
test-windows (engine dask, python 3.8, group_1)	3m 42s
test-windows (engine dask, python 3.8, group_2)	3m 44s
test-windows (engine dask, python 3.8, group_3)	3m 42s
test-windows (engine dask, python 3.8, group_4)	3m 40s
test experimental	9m 22s
Test HDK storage format, Python 3.8	22m 23s
test-internals	7m 45s
test (pyarrow, python 3.8)	4m 38s
test-spreadsheet (engine ray, python 3.8)	3m 47s
test-spreadsheet (engine dask, python 3.8)	3m 57s
test-asv-benchmarks	0s
test-ubuntu (engine unidist mpi, python 3.8)	1h 1m 9s
upload-coverage	0s
	3h 30m 29s

Provide feedback