TYP: Narrow down type of method keyword in Index (#52723)

* Add literal type hint. * Move type variable to _typing.py. * Use existing type alias. * EOF

Author: kklein

pandas/core/indexes/base.py

@@ -56,6 +56,7 @@
  JoinHow,
  Level,
  NaPosition,
+ ReindexMethod,
  Self,
  Shape,
  npt,
@@ -208,7 +209,6 @@
 _index_shared_docs: dict[str, str] = {}
 str_t = str
 
-
 _dtype_obj = np.dtype("object")
 
 _masked_engines = {
@@ -3746,7 +3746,7 @@ def get_loc(self, key):
  def get_indexer(
  self,
  target,
- method: str_t | None = None,
+ method: ReindexMethod | None = None,
  limit: int | None = None,
  tolerance=None,
  ) -> npt.NDArray[np.intp]:
@@ -4199,7 +4199,7 @@ def _validate_can_reindex(self, indexer: np.ndarray) -> None:
  def reindex(
  self,
  target,
- method=None,
+ method: ReindexMethod | None = None,
  level=None,
  limit: int | None = None,
  tolerance: float | None = None,