searchsorted numpy compat for Period dtype (pandas-dev#36254)

Author: jbrockmendel

doc/source/whatsnew/v1.2.0.rst

@@ -228,7 +228,7 @@ Datetimelike
 - Bug in :class:`DateOffset` where attributes reconstructed from pickle files differ from original objects when input values exceed normal ranges (e.g months=12) (:issue:`34511`)
 - Bug in :meth:`DatetimeIndex.get_slice_bound` where ``datetime.date`` objects were not accepted or naive :class:`Timestamp` with a tz-aware :class:`DatetimeIndex` (:issue:`35690`)
 - Bug in :meth:`DatetimeIndex.slice_locs` where ``datetime.date`` objects were not accepted (:issue:`34077`)
-- Bug in :meth:`DatetimeIndex.searchsorted`, :meth:`TimedeltaIndex.searchsorted`, and :meth:`Series.searchsorted` with ``datetime64`` or ``timedelta64`` dtype placement of ``NaT`` values being inconsistent with ``NumPy`` (:issue:`36176`)
+- Bug in :meth:`DatetimeIndex.searchsorted`, :meth:`TimedeltaIndex.searchsorted`, :meth:`PeriodIndex.searchsorted`, and :meth:`Series.searchsorted` with ``datetime64``, ``timedelta64`` or ``Period`` dtype placement of ``NaT`` values being inconsistent with ``NumPy`` (:issue:`36176`,:issue:`36254`)
 
 Timedelta
 ^^^^^^^^^

pandas/core/arrays/period.py

@@ -587,6 +587,13 @@ def astype(self, dtype, copy: bool = True):
             return self.asfreq(dtype.freq)
         return super().astype(dtype, copy=copy)
 
+    def searchsorted(self, value, side="left", sorter=None):
+        value = self._validate_searchsorted_value(value).view("M8[ns]")
+
+        # Cast to M8 to get datetime-like NaT placement
+        m8arr = self._ndarray.view("M8[ns]")
+        return m8arr.searchsorted(value, side=side, sorter=sorter)
+
     # ------------------------------------------------------------------
     # Arithmetic Methods
 

pandas/tests/arrays/test_datetimelike.py

@@ -244,7 +244,7 @@ def test_searchsorted(self):
         # GH#29884 match numpy convention on whether NaT goes
         #  at the end or the beginning
         result = arr.searchsorted(pd.NaT)
-        if np_version_under1p18 or self.array_cls is PeriodArray:
+        if np_version_under1p18:
             # Following numpy convention, NaT goes at the beginning
             #  (unlike NaN which goes at the end)
             assert result == 0

pandas/tests/indexes/period/test_searchsorted.py

@@ -2,6 +2,7 @@
 import pytest
 
 from pandas._libs.tslibs import IncompatibleFrequency
+from pandas.compat.numpy import np_version_under1p18
 
 from pandas import NaT, Period, PeriodIndex, Series, array
 import pandas._testing as tm
@@ -21,7 +22,13 @@ def test_searchsorted(self, freq):
         p2 = Period("2014-01-04", freq=freq)
         assert pidx.searchsorted(p2) == 3
 
-        assert pidx.searchsorted(NaT) == 0
+        if np_version_under1p18:
+            # GH#36254
+            # Following numpy convention, NaT goes at the beginning
+            #  (unlike NaN which goes at the end)
+            assert pidx.searchsorted(NaT) == 0
+        else:
+            assert pidx.searchsorted(NaT) == 5
 
         msg = "Input has different freq=H from PeriodArray"
         with pytest.raises(IncompatibleFrequency, match=msg):