CLN: rename lib.isscalar to lib.is_scalar

[databasedav]

• closes CLN: rename lib.isscalar to lib.is_scalar #18987
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

There's also a handful of methods which call is_scalar that are named isscalar, e.g.:

pandas/pandas/core/computation/ops.py

Lines 101 to 103 in 8433562

	@property
	def isscalar(self):
	return is_scalar(self._value)

should these be changed as well?

Also does a CLN require an entry in whatsnew?

[jbrockmendel]

+1. This has bothered me for a while.

[codecov]

Codecov Report

Merging #19000 into master will not change coverage.
The diff coverage is 75%.

@@           Coverage Diff           @@
##           master   #19000   +/-   ##
=======================================
  Coverage   91.58%   91.58%           
=======================================
  Files         150      150           
  Lines       48972    48972           
=======================================
  Hits        44851    44851           
  Misses       4121     4121

Flag	Coverage Δ
#multiple	89.94% <75%> (ø)	⬆️
#single	41.72% <25%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/algorithms.py	94.14% <0%> (ø)	⬆️
pandas/core/dtypes/inference.py	98.36% <100%> (ø)	⬆️
pandas/core/indexes/datetimelike.py	97.04% <100%> (ø)	⬆️
pandas/core/indexes/base.py	96.45% <100%> (ø)	⬆️

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[jreback]

you can change isscalar as you pointed above (and other instances as appropriate). making things more clear / consistent is the goal. don't need a whatsnew here as this is an internal change.

[jreback]

lgtm. note that windows is currently failing, but ping when travis ci is green.

[jreback]

thanks @gitavi