BUG: PeriodEngine doesn't work (#29038)

Author: proost

pandas/_libs/index.pyx

@@ -25,6 +25,8 @@ from pandas._libs.hashtable cimport HashTable
 from pandas._libs import algos, hashtable as _hash
 from pandas._libs.tslibs import Timestamp, Timedelta, period as periodlib
 from pandas._libs.missing import checknull
+from pandas._libs.tslibs.util cimport is_period_object
+
 
 cdef int64_t NPY_NAT = util.get_nat()
 
@@ -498,7 +500,7 @@ cdef class TimedeltaEngine(DatetimeEngine):
 cdef class PeriodEngine(Int64Engine):
 
     cdef _get_index_values(self):
-        return super(PeriodEngine, self).vgetter()
+        return super(PeriodEngine, self).vgetter().view('i8')
 
     cpdef _call_map_locations(self, values):
         super(PeriodEngine, self)._call_map_locations(values.view('i8'))
@@ -537,6 +539,43 @@ cdef class PeriodEngine(Int64Engine):
 
         return super(PeriodEngine, self).get_indexer_non_unique(ordinal_array)
 
+    cpdef get_loc(self, object key):
+        cdef:
+            int64_t loc
+        if is_definitely_invalid_key(key):
+            raise TypeError("'{val}' is an invalid key".format(val=key))
+
+        ordinal = key.ordinal if is_period_object(key) else key
+        self._ordinal_check_type(key, ordinal)
+
+        if self.over_size_threshold and self.is_monotonic_increasing:
+            if not self.is_unique:
+                return self._get_loc_duplicates(key)
+
+            values = self._get_index_values()
+
+            try:
+                loc = values.searchsorted(ordinal, side='left')
+            except TypeError:
+                raise KeyError(key)
+
+            if loc == len(values) or values[loc] != ordinal:
+                raise KeyError(key)
+            return loc
+
+        self._ensure_mapping_populated()
+        if not self.unique:
+            return self._get_loc_duplicates(ordinal)
+
+        try:
+            return self.mapping.get_item(ordinal)
+        except KeyError:
+            raise KeyError(key)
+
+    cdef inline _ordinal_check_type(self, object key, ordinal):
+        if not util.is_integer_object(ordinal):
+            raise KeyError(key)
+
 
 cpdef convert_scalar(ndarray arr, object value):
     # we don't turn integers

pandas/tests/indexes/period/test_indexing.py

@@ -685,3 +685,13 @@ def test_period_index_indexer(self):
         tm.assert_frame_equal(df, df.loc[list(idx)])
         tm.assert_frame_equal(df.iloc[0:5], df.loc[idx[0:5]])
         tm.assert_frame_equal(df, df.loc[list(idx)])
+
+    def test_period_engine_get_loc_accept_period(self):
+        # issue 29038
+        idx = pd.period_range(start=2010, end=2019, freq="A")
+        assert idx._engine.get_loc(Period(2015)) == 5
+
+        with pytest.raises(KeyError, match=r"Period\('2020', 'A-DEC'\)"):
+            idx._engine.get_loc(Period(2020))
+
+        assert idx._engine.get_loc(Period(2018).ordinal) == 8