REF: move casting from Index._get_indexer to Index.get_indexer (#42308)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -3486,6 +3486,18 @@ def get_indexer(
             # Only call equals if we have same dtype to avoid inference/casting
             return np.arange(len(target), dtype=np.intp)
 
+        if not is_dtype_equal(self.dtype, target.dtype) and not is_interval_dtype(
+            self.dtype
+        ):
+            # IntervalIndex gets special treatment for partial-indexing
+            dtype = self._find_common_type_compat(target)
+
+            this = self.astype(dtype, copy=False)
+            target = target.astype(dtype, copy=False)
+            return this._get_indexer(
+                target, method=method, limit=limit, tolerance=tolerance
+            )
+
         return self._get_indexer(target, method, limit, tolerance)
 
     def _get_indexer(
@@ -3498,15 +3510,6 @@ def _get_indexer(
         if tolerance is not None:
             tolerance = self._convert_tolerance(tolerance, target)
 
-        if not is_dtype_equal(self.dtype, target.dtype):
-            dtype = self._find_common_type_compat(target)
-
-            this = self.astype(dtype, copy=False)
-            target = target.astype(dtype, copy=False)
-            return this.get_indexer(
-                target, method=method, limit=limit, tolerance=tolerance
-            )
-
         if method in ["pad", "backfill"]:
             indexer = self._get_fill_indexer(target, method, limit, tolerance)
         elif method == "nearest":

pandas/core/indexes/range.py

@@ -409,10 +409,6 @@ def _get_indexer(
             reverse = self._range[::-1]
             start, stop, step = reverse.start, reverse.stop, reverse.step
 
-        if not is_signed_integer_dtype(target):
-            # checks/conversions/roundings are delegated to general method
-            return super()._get_indexer(target, method=method, tolerance=tolerance)
-
         target_array = np.asarray(target)
         locs = target_array - start
         valid = (locs % step == 0) & (locs >= 0) & (target_array < stop)