PERF: Fixed perf regression in TimedeltaIndex.get_loc

Closes pandas-dev#34510

Author: TomAugspurger

doc/source/whatsnew/v1.1.0.rst

@@ -760,6 +760,7 @@ Deprecations
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
+- Fixed performance regression in :meth:`TimedeltaIndex.get_loc` (:issue:`34510`)
 - Performance improvement in :class:`Timedelta` constructor (:issue:`30543`)
 - Performance improvement in :class:`Timestamp` constructor (:issue:`30543`)
 - Performance improvement in flex arithmetic ops between :class:`DataFrame` and :class:`Series` with ``axis=0`` (:issue:`31296`)

pandas/core/arrays/datetimelike.py

@@ -776,15 +776,19 @@ def _validate_shift_value(self, fill_value):
 
         return self._unbox(fill_value)
 
-    def _validate_scalar(self, value, msg: str, cast_str: bool = False):
+    def _validate_scalar(
+        self, value, msg: Optional[str] = None, cast_str: bool = False
+    ):
         """
         Validate that the input value can be cast to our scalar_type.
 
         Parameters
         ----------
         value : object
-        msg : str
+        msg : str, optional.
             Message to raise in TypeError on invalid input.
+            If not provided, `value` is cast to a str and used
+            as the message.
         cast_str : bool, default False
             Whether to try to parse string input to scalar_type.
 
@@ -807,6 +811,8 @@ def _validate_scalar(self, value, msg: str, cast_str: bool = False):
             value = self._scalar_type(value)  # type: ignore
 
         else:
+            if msg is None:
+                msg = str(value)
             raise TypeError(msg)
 
         return value

pandas/core/indexes/timedeltas.py

@@ -212,9 +212,8 @@ def get_loc(self, key, method=None, tolerance=None):
         if not is_scalar(key):
             raise InvalidIndexError(key)
 
-        msg = str(key)
         try:
-            key = self._data._validate_scalar(key, msg, cast_str=True)
+            key = self._data._validate_scalar(key, cast_str=True)
         except TypeError as err:
             raise KeyError(key) from err