Fix zillion deprecation warnings in core.dtypes.common

[jbrockmendel]

Looking through a recent Travis log I see tons of these:

  /home/travis/build/pandas-dev/pandas/pandas/core/dtypes/common.py:2026: DeprecationWarning: elementwise == comparison failed; this will raise an error in the future.
    if dtype in [object, np.object_, 'object', 'O']:

This is driven by (probably not desired) cases where dtype is array-like at this point (also showed up in #22092). Easily avoided by checking for hashability before checking for inclusion.

[pep8speaks]

Hello @jbrockmendel! Thanks for updating the PR.

Cheers ! There are no PEP8 issues in this Pull Request. 🍻

Comment last updated on July 31, 2018 at 17:39 Hours UTC

[jreback]

this is #22101

[codecov]

Codecov Report

Merging #22142 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #22142      +/-   ##
==========================================
- Coverage   92.07%   92.06%   -0.01%     
==========================================
  Files         170      170              
  Lines       50688    50689       +1     
==========================================
- Hits        46671    46669       -2     
- Misses       4017     4020       +3

Flag	Coverage Δ
#multiple	90.47% <100%> (-0.01%)	⬇️
#single	42.29% <100%> (-0.03%)	⬇️

Impacted Files	Coverage Δ
pandas/core/dtypes/common.py	94.87% <100%> (-0.34%)	⬇️
pandas/util/testing.py	85.69% <0%> (-0.21%)	⬇️
pandas/core/arrays/datetimes.py	95.44% <0%> (-0.03%)	⬇️
pandas/core/dtypes/dtypes.py	96.05% <0%> (+0.02%)	⬆️
pandas/core/indexes/period.py	93.5% <0%> (+0.1%)	⬆️

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[jreback]

thanks!