CLN: defer CategoricalIndex.astype to Categorical.astype (#37908)

Author: jbrockmendel

pandas/core/arrays/categorical.py

@@ -405,12 +405,12 @@ def astype(self, dtype: Dtype, copy: bool = True) -> ArrayLike:
  if is_categorical_dtype(dtype):
  dtype = cast(Union[str, CategoricalDtype], dtype)
 
- # GH 10696/18593
+ # GH 10696/18593/18630
  dtype = self.dtype.update_dtype(dtype)
- self = self.copy() if copy else self
+ result = self.copy() if copy else self
  if dtype == self.dtype:
- return self
- return self._set_dtype(dtype)
+ return result
+ return result._set_dtype(dtype)
  if is_extension_array_dtype(dtype):
  return array(self, dtype=dtype, copy=copy)
  if is_integer_dtype(dtype) and self.isna().any():

pandas/core/indexes/category.py

@@ -14,10 +14,8 @@
 from pandas.core.dtypes.common import (
  ensure_platform_int,
  is_categorical_dtype,
- is_interval_dtype,
  is_list_like,
  is_scalar,
- pandas_dtype,
 )
 from pandas.core.dtypes.dtypes import CategoricalDtype
 from pandas.core.dtypes.missing import is_valid_nat_for_dtype, isna, notna
@@ -370,20 +368,8 @@ def __contains__(self, key: Any) -> bool:
 
  @doc(Index.astype)
  def astype(self, dtype, copy=True):
- if dtype is not None:
- dtype = pandas_dtype(dtype)
-
- if is_interval_dtype(dtype):
- from pandas import IntervalIndex
-
- return IntervalIndex(np.array(self))
- elif is_categorical_dtype(dtype):
- # GH 18630
- dtype = self.dtype.update_dtype(dtype)
- if dtype == self.dtype:
- return self.copy() if copy else self
-
- return Index.astype(self, dtype=dtype, copy=copy)
+ res_data = self._data.astype(dtype, copy=copy)
+ return Index(res_data, name=self.name)
 
  @doc(Index.fillna)
  def fillna(self, value, downcast=None):