REF: share _get_string_slice (#42149)

Author: jbrockmendel

pandas/_libs/tslibs/parsing.pyx

@@ -470,8 +470,7 @@ cdef inline object _parse_dateabbr_string(object date_string, datetime default,
     except ValueError:
         pass
 
-    if date_len == 6 and (freq == 'M' or
-                          getattr(freq, 'rule_code', None) == 'M'):
+    if date_len == 6 and freq == 'M':
         year = int(date_string[:4])
         month = int(date_string[4:6])
         try:

pandas/core/indexes/datetimelike.py

@@ -26,6 +26,7 @@
     NaTType,
     Resolution,
     Tick,
+    parsing,
 )
 from pandas._typing import (
     Callable,
@@ -399,9 +400,22 @@ def _summary(self, name=None) -> str:
     def _validate_partial_date_slice(self, reso: Resolution):
         raise NotImplementedError
 
-    def _parsed_string_to_bounds(self, reso: Resolution, parsed: datetime):
+    def _parsed_string_to_bounds(self, reso: Resolution, parsed):
         raise NotImplementedError
 
+    def _parse_with_reso(self, label: str):
+        # overridden by TimedeltaIndex
+        parsed, reso_str = parsing.parse_time_string(label, self.freq)
+        reso = Resolution.from_attrname(reso_str)
+        return parsed, reso
+
+    def _get_string_slice(self, key: str):
+        parsed, reso = self._parse_with_reso(key)
+        try:
+            return self._partial_date_slice(reso, parsed)
+        except KeyError as err:
+            raise KeyError(key) from err
+
     @final
     def _partial_date_slice(
         self,

pandas/core/indexes/datetimes.py

@@ -726,13 +726,11 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
         self._deprecated_arg(kind, "kind", "_maybe_cast_slice_bound")
 
         if isinstance(label, str):
-            freq = getattr(self, "freqstr", getattr(self, "inferred_freq", None))
             try:
-                parsed, reso_str = parsing.parse_time_string(label, freq)
+                parsed, reso = self._parse_with_reso(label)
             except parsing.DateParseError as err:
                 raise self._invalid_indexer("slice", label) from err
 
-            reso = Resolution.from_attrname(reso_str)
             lower, upper = self._parsed_string_to_bounds(reso, parsed)
             # lower, upper form the half-open interval:
             #   [parsed, parsed + 1 freq)
@@ -750,12 +748,6 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
 
         return self._maybe_cast_for_get_loc(label)
 
-    def _get_string_slice(self, key: str):
-        freq = getattr(self, "freqstr", getattr(self, "inferred_freq", None))
-        parsed, reso_str = parsing.parse_time_string(key, freq)
-        reso = Resolution.from_attrname(reso_str)
-        return self._partial_date_slice(reso, parsed)
-
     def slice_indexer(self, start=None, end=None, step=None, kind=None):
         """
         Return indexer for specified label slice.

pandas/core/indexes/period.py

@@ -479,12 +479,11 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
             return Period(label, freq=self.freq)
         elif isinstance(label, str):
             try:
-                parsed, reso_str = parse_time_string(label, self.freq)
+                parsed, reso = self._parse_with_reso(label)
             except ValueError as err:
                 # string cannot be parsed as datetime-like
                 raise self._invalid_indexer("slice", label) from err
 
-            reso = Resolution.from_attrname(reso_str)
             lower, upper = self._parsed_string_to_bounds(reso, parsed)
             return lower if side == "left" else upper
         elif not isinstance(label, self._data._recognized_scalars):
@@ -508,14 +507,6 @@ def _validate_partial_date_slice(self, reso: Resolution):
             #  why is that check not needed?
             raise ValueError
 
-    def _get_string_slice(self, key: str):
-        parsed, reso_str = parse_time_string(key, self.freq)
-        reso = Resolution.from_attrname(reso_str)
-        try:
-            return self._partial_date_slice(reso, parsed)
-        except KeyError as err:
-            raise KeyError(key) from err
-
 
 def period_range(
     start=None, end=None, periods: int | None = None, freq=None, name=None

pandas/core/indexes/timedeltas.py

@@ -108,6 +108,9 @@ class TimedeltaIndex(DatetimeTimedeltaMixin):
 
     _data: TimedeltaArray
 
+    # Use base class method instead of DatetimeTimedeltaMixin._get_string_slice
+    _get_string_slice = Index._get_string_slice
+
     # -------------------------------------------------------------------
     # Constructors
 
@@ -197,20 +200,29 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
 
         if isinstance(label, str):
             try:
-                parsed = Timedelta(label)
+                parsed, reso = self._parse_with_reso(label)
             except ValueError as err:
                 # e.g. 'unit abbreviation w/o a number'
                 raise self._invalid_indexer("slice", label) from err
 
-            # The next two lines are analogous to DTI/PI._parsed_str_to_bounds
-            lower = parsed.round(parsed.resolution_string)
-            upper = lower + to_offset(parsed.resolution_string) - Timedelta(1, "ns")
+            lower, upper = self._parsed_string_to_bounds(reso, parsed)
             return lower if side == "left" else upper
         elif not isinstance(label, self._data._recognized_scalars):
             raise self._invalid_indexer("slice", label)
 
         return label
 
+    def _parse_with_reso(self, label: str):
+        # the "with_reso" is a no-op for TimedeltaIndex
+        parsed = Timedelta(label)
+        return parsed, None
+
+    def _parsed_string_to_bounds(self, reso, parsed: Timedelta):
+        # reso is unused, included to match signature of DTI/PI
+        lbound = parsed.round(parsed.resolution_string)
+        rbound = lbound + to_offset(parsed.resolution_string) - Timedelta(1, "ns")
+        return lbound, rbound
+
     # -------------------------------------------------------------------
 
     @property