BUG: Allow string keys with higher resolution than index in PeriodIndex.get_loc

doc/source/whatsnew/v1.4.0.rst

@@ -289,6 +289,7 @@ Indexing
 - Bug in :meth:`Index.get_indexer_non_unique` when index contains multiple ``np.nan`` (:issue:`35392`)
 - Bug in :meth:`DataFrame.query` did not handle the degree sign in a backticked column name, such as \`Temp(°C)\`, used in an expression to query a dataframe (:issue:`42826`)
 - Bug in :meth:`DataFrame.drop` where the error message did not show missing labels with commas when raising ``KeyError`` (:issue:`42881`)
+- Bug in :meth:`PeriodIndex.get_loc` raised ``KeyError`` with string key corresponding to higher resolution than the index (:issue:`40145`)
 -
 
 Missing

pandas/core/indexes/period.py

@@ -427,15 +427,14 @@ def get_loc(self, key, method=None, tolerance=None):
                     raise KeyError(key) from err
 
             if reso == self.dtype.resolution:
-                # the reso < self.dtype.resolution case goes through _get_string_slice
+                # the reso > self.dtype.resolution case goes through _partial_date_slice
                 key = Period(parsed, freq=self.freq)
                 loc = self.get_loc(key, method=method, tolerance=tolerance)
                 # Recursing instead of falling through matters for the exception
                 #  message in test_get_loc3 (though not clear if that really matters)
                 return loc
-            elif method is None:
-                raise KeyError(key)
-            else:
+            elif reso < self.dtype.resolution:
+                # GH 40145 Fall through
                 key = Period(parsed, freq=self.freq)
 
         elif isinstance(key, Period):

pandas/tests/indexes/period/test_indexing.py

@@ -213,37 +213,29 @@ def test_getitem_seconds(self):
 
     def test_getitem_day(self):
         # GH#6716
-        # Confirm DatetimeIndex and PeriodIndex works identically
         didx = date_range(start="2013/01/01", freq="D", periods=400)
         pidx = period_range(start="2013/01/01", freq="D", periods=400)
 
+        # Identitcal for DatetimeIndex and PeriodIndex
         for idx in [didx, pidx]:
-            # getitem against index should raise ValueError
-            values = [
-                "2014",
-                "2013/02",
-                "2013/01/02",
-                "2013/02/01 9H",
-                "2013/02/01 09:00",
-            ]
-            for v in values:
-
-                # GH7116
-                # these show deprecations as we are trying
-                # to slice with non-integer indexers
-                # with pytest.raises(IndexError):
-                #    idx[v]
-                continue
-
             s = Series(np.random.rand(len(idx)), index=idx)
             tm.assert_series_equal(s["2013/01"], s[0:31])
             tm.assert_series_equal(s["2013/02"], s[31:59])
             tm.assert_series_equal(s["2014"], s[365:])
 
-            invalid = ["2013/02/01 9H", "2013/02/01 09:00"]
-            for v in invalid:
-                with pytest.raises(KeyError, match=v):
-                    s[v]
+        higher_reso = ["2013/02/01 9H", "2013/02/01 09:00"]
+
+        # DatetimeIndex raises
+        s = Series(np.random.rand(len(didx)), index=didx)
+        for v in higher_reso:
+            with pytest.raises(KeyError, match=v):
+                s[v]
+
+        # GH 40145 PeriodIndex works
+        s = Series(np.random.rand(len(pidx)), index=pidx)
+        for v in higher_reso:
+            assert v in pidx
+            assert s[v] == s[31]
 
 
 class TestGetLoc:
@@ -883,15 +875,10 @@ def test_contains(self):
             assert p in idx0
             assert str(p) in idx0
 
-        # GH#31172
-        # Higher-resolution period-like are _not_ considered as contained
         key = "2017-09-01 00:00:01"
-        assert key not in idx0
-        with pytest.raises(KeyError, match=key):
-            idx0.get_loc(key)
-        with pytest.raises(KeyError, match=key):
-            with tm.assert_produces_warning(FutureWarning):
-                idx0.get_value(ser, key)
+        assert key in idx0
+        with tm.assert_produces_warning(FutureWarning):
+            idx0.get_value(ser, key)
 
         assert "2017-09" in idx0