REF: _validate_partial_date_slice -> _can_partial_date_slice (#42225)

Author: jbrockmendel

pandas/core/indexes/datetimelike.py

@@ -282,7 +282,7 @@ def _summary(self, name=None) -> str:
     # --------------------------------------------------------------------
     # Indexing Methods
 
-    def _validate_partial_date_slice(self, reso: Resolution):
+    def _can_partial_date_slice(self, reso: Resolution) -> bool:
         raise NotImplementedError
 
     def _parsed_string_to_bounds(self, reso: Resolution, parsed):
@@ -317,7 +317,8 @@ def _partial_date_slice(
         -------
         slice or ndarray[intp]
         """
-        self._validate_partial_date_slice(reso)
+        if not self._can_partial_date_slice(reso):
+            raise ValueError
 
         t1, t2 = self._parsed_string_to_bounds(reso, parsed)
         vals = self._data._ndarray

pandas/core/indexes/datetimes.py

@@ -603,7 +603,7 @@ def _parsed_string_to_bounds(self, reso: Resolution, parsed: datetime):
             end = end.tz_localize(self.tz)
         return start, end
 
-    def _validate_partial_date_slice(self, reso: Resolution):
+    def _can_partial_date_slice(self, reso: Resolution) -> bool:
         assert isinstance(reso, Resolution), (type(reso), reso)
         if (
             self.is_monotonic
@@ -614,12 +614,13 @@ def _validate_partial_date_slice(self, reso: Resolution):
             # GH3452 and GH2369.
 
             # See also GH14826
-            raise KeyError
+            return False
 
         if reso.attrname == "microsecond":
             # _partial_date_slice doesn't allow microsecond resolution, but
             # _parsed_string_to_bounds allows it.
-            raise KeyError
+            return False
+        return True
 
     def _deprecate_mismatched_indexing(self, key) -> None:
         # GH#36148
@@ -663,14 +664,22 @@ def get_loc(self, key, method=None, tolerance=None):
             key = self._maybe_cast_for_get_loc(key)
 
         elif isinstance(key, str):
+
             try:
-                return self._get_string_slice(key)
-            except (TypeError, KeyError, ValueError, OverflowError):
-                pass
+                parsed, reso = self._parse_with_reso(key)
+            except ValueError as err:
+                raise KeyError(key) from err
 
+            if self._can_partial_date_slice(reso):
+                try:
+                    return self._partial_date_slice(reso, parsed)
+                except KeyError as err:
+                    if method is None:
+                        raise KeyError(key) from err
             try:
                 key = self._maybe_cast_for_get_loc(key)
             except ValueError as err:
+                # FIXME: we get here because parse_with_reso doesn't raise on "t2m"
                 raise KeyError(key) from err
 
         elif isinstance(key, timedelta):

pandas/core/indexes/period.py

@@ -15,14 +15,11 @@
 )
 from pandas._libs.tslibs import (
     BaseOffset,
+    NaT,
     Period,
     Resolution,
     Tick,
 )
-from pandas._libs.tslibs.parsing import (
-    DateParseError,
-    parse_time_string,
-)
 from pandas._typing import (
     Dtype,
     DtypeObj,
@@ -35,6 +32,7 @@
     pandas_dtype,
 )
 from pandas.core.dtypes.dtypes import PeriodDtype
+from pandas.core.dtypes.missing import is_valid_na_for_dtype
 
 from pandas.core.arrays.period import (
     PeriodArray,
@@ -409,43 +407,50 @@ def get_loc(self, key, method=None, tolerance=None):
         orig_key = key
 
         self._check_indexing_error(key)
-        if isinstance(key, str):
 
-            try:
-                loc = self._get_string_slice(key)
-                return loc
-            except (TypeError, ValueError):
-                pass
+        if is_valid_na_for_dtype(key, self.dtype):
+            key = NaT
+
+        elif isinstance(key, str):
 
             try:
-                asdt, reso_str = parse_time_string(key, self.freq)
-            except (ValueError, DateParseError) as err:
+                parsed, reso = self._parse_with_reso(key)
+            except ValueError as err:
                 # A string with invalid format
                 raise KeyError(f"Cannot interpret '{key}' as period") from err
 
-            reso = Resolution.from_attrname(reso_str)
+            if self._can_partial_date_slice(reso):
+                try:
+                    return self._partial_date_slice(reso, parsed)
+                except KeyError as err:
+                    # TODO: pass if method is not None, like DTI does?
+                    raise KeyError(key) from err
 
             if reso == self.dtype.resolution:
                 # the reso < self.dtype.resolution case goes through _get_string_slice
-                key = Period(asdt, freq=self.freq)
+                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:
-                key = asdt
+                key = Period(parsed, freq=self.freq)
 
-        elif is_integer(key):
-            # Period constructor will cast to string, which we dont want
-            raise KeyError(key)
         elif isinstance(key, Period) and key.freq != self.freq:
             raise KeyError(key)
-
-        try:
-            key = Period(key, freq=self.freq)
-        except ValueError as err:
-            # we cannot construct the Period
-            raise KeyError(orig_key) from err
+        elif isinstance(key, Period):
+            pass
+        elif isinstance(key, datetime):
+            try:
+                key = Period(key, freq=self.freq)
+            except ValueError as err:
+                # we cannot construct the Period
+                raise KeyError(orig_key) from err
+        else:
+            # in particular integer, which Period constructor would cast to string
+            raise KeyError(key)
 
         try:
             return Index.get_loc(self, key, method, tolerance)
@@ -496,7 +501,7 @@ def _parsed_string_to_bounds(self, reso: Resolution, parsed: datetime):
         iv = Period(parsed, freq=grp.value)
         return (iv.asfreq(self.freq, how="start"), iv.asfreq(self.freq, how="end"))
 
-    def _validate_partial_date_slice(self, reso: Resolution):
+    def _can_partial_date_slice(self, reso: Resolution) -> bool:
         assert isinstance(reso, Resolution), (type(reso), reso)
         grp = reso.freq_group
         freqn = self.dtype.freq_group_code
@@ -505,7 +510,9 @@ def _validate_partial_date_slice(self, reso: Resolution):
             # TODO: we used to also check for
             #  reso in ["day", "hour", "minute", "second"]
             #  why is that check not needed?
-            raise ValueError
+            return False
+
+        return True
 
 
 def period_range(