Literal typing for indexer methods (#52729)

* typing for indexer methods

* more literal typing for na_position for range

* another na_position to be typed

* use NaPosition in pandas._typing

Author: emptymalei

pandas/core/indexes/base.py

@@ -55,6 +55,7 @@
     IndexLabel,
     JoinHow,
     Level,
+    NaPosition,
     Self,
     Shape,
     npt,
@@ -1921,7 +1922,7 @@ def sortlevel(
         level=None,
         ascending: bool | list[bool] = True,
         sort_remaining=None,
-        na_position: str_t = "first",
+        na_position: NaPosition = "first",
     ):
         """
         For internal compatibility with the Index API.
@@ -5573,7 +5574,7 @@ def sort_values(
         self,
         return_indexer: bool = False,
         ascending: bool = True,
-        na_position: str_t = "last",
+        na_position: NaPosition = "last",
         key: Callable | None = None,
     ):
         """
@@ -6168,7 +6169,7 @@ def groupby(self, values) -> PrettyDict[Hashable, np.ndarray]:
 
         return PrettyDict(result)
 
-    def map(self, mapper, na_action=None):
+    def map(self, mapper, na_action: Literal["ignore"] | None = None):
         """
         Map values using an input mapping or function.
 

pandas/core/indexes/range.py

@@ -50,6 +50,7 @@
 if TYPE_CHECKING:
     from pandas._typing import (
         Dtype,
+        NaPosition,
         Self,
         npt,
     )
@@ -493,7 +494,7 @@ def sort_values(
         self,
         return_indexer: bool = False,
         ascending: bool = True,
-        na_position: str = "last",
+        na_position: NaPosition = "last",
         key: Callable | None = None,
     ):
         if key is not None: