BUG: Inconsistency between PeriodIndex.get_value vs get_loc

pandas/core/indexes/period.py

@@ -567,12 +567,33 @@ def get_loc(self, key, method=None, tolerance=None):
         """
 
         if isinstance(key, str):
+
             try:
-                asdt, reso = parse_time_string(key, self.freq)
-                key = asdt
-            except DateParseError:
-                # A string with invalid format
-                raise KeyError(f"Cannot interpret '{key}' as period")
+                loc = self._get_string_slice(key)
+                return loc
+            except (TypeError, ValueError):
+
+                try:
+                    asdt, reso = parse_time_string(key, self.freq)
+                except DateParseError:
+                    # A string with invalid format
+                    raise KeyError(f"Cannot interpret '{key}' as period")
+
+                grp = resolution.Resolution.get_freq_group(reso)
+                freqn = resolution.get_freq_group(self.freq)
+
+                # _get_string_slice will handle cases where grp < freqn
+                assert grp >= freqn
+
+                if grp == freqn:
+                    key = Period(asdt, freq=self.freq)
+                    loc = self.get_loc(key, method=method, tolerance=tolerance)
+                    # TODO: or better just to let fall through?
+                    return loc
+                elif method is None:
+                    raise KeyError(key)
+                else:
+                    key = asdt
 
         elif is_integer(key):
             # Period constructor will cast to string, which we dont want

pandas/tests/indexes/period/test_indexing.py

@@ -518,12 +518,19 @@ def test_contains(self):
 
         ps0 = [p0, p1, p2]
         idx0 = pd.PeriodIndex(ps0)
+        ser = pd.Series(range(6, 9), index=idx0)
 
         for p in ps0:
             assert p in idx0
             assert str(p) in idx0
 
-        assert "2017-09-01 00:00:01" in idx0
+        # 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):
+            idx0.get_value(ser, key)
 
         assert "2017-09" in idx0