REF: SparseArray imports

[TomAugspurger]

arrays/sparse.py was doing an import pandas as pd, which is prone to cause circular imports. I've eliminated that import and updated the namespaces appropriately (NaT, isna, algos.unique / factorize).

Also updated setup.cfg to check the import order in arrays/sparse.py.

[pep8speaks]

Hello @TomAugspurger! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/arrays/sparse.py !

• There are no PEP8 issues in the file pandas/core/series.py !

[alimcmaster1]

LGTM - thanks for cleaning up the imports using isort too :)

[alimcmaster1]

I think if you remove one of the newlines after from pandas.errors import PerformanceWarning in sparse.py that should fix the isort failure on CI :)

[codecov]

Codecov Report

Merging #23329 into master will not change coverage.
The diff coverage is 96%.

@@           Coverage Diff           @@
##           master   #23329   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         169      169           
  Lines       51258    51258           
=======================================
  Hits        47274    47274           
  Misses       3984     3984

Flag	Coverage Δ
#multiple	90.66% <96%> (ø)	⬆️
#single	42.23% <64%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/series.py	93.91% <100%> (-0.01%)	⬇️
pandas/core/arrays/sparse.py	91.84% <95.83%> (ø)	⬆️
pandas/core/arrays/datetimes.py	97.46% <0%> (ø)	⬆️

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[TomAugspurger]

Thanks.

Merging tonight, since this is a straight refactor, and I have another PR building on top if it.

[jreback]

pls merge master ping on green.

[TomAugspurger]

CircleCI seems to be ~10 hours behind. OK to cancel those, since we're dropping (most) of them anyway? I'll be free to clean things up this afternoon if we accidentally break anything.

[jreback]

sure