TYP: Add typing.overload signatures to DataFrame.drop_duplicates. (#54281)

* TYP: Add typing.overload signatures to DataFrame.drop_duplicates.

This adds overloads so that a type checker can determine whether
drop_duplicates returns DataFrame or None based on the value of the
`inplace` argument.

* Use 4-space indent.

Author: rchen152

pandas/core/frame.py

@@ -6383,6 +6383,39 @@ def dropna(
         self._update_inplace(result)
         return None
 
+    @overload
+    def drop_duplicates(
+        self,
+        subset: Hashable | Sequence[Hashable] | None = ...,
+        *,
+        keep: DropKeep = ...,
+        inplace: Literal[True],
+        ignore_index: bool = ...,
+    ) -> None:
+        ...
+
+    @overload
+    def drop_duplicates(
+        self,
+        subset: Hashable | Sequence[Hashable] | None = ...,
+        *,
+        keep: DropKeep = ...,
+        inplace: Literal[False] = ...,
+        ignore_index: bool = ...,
+    ) -> DataFrame:
+        ...
+
+    @overload
+    def drop_duplicates(
+        self,
+        subset: Hashable | Sequence[Hashable] | None = ...,
+        *,
+        keep: DropKeep = ...,
+        inplace: bool = ...,
+        ignore_index: bool = ...,
+    ) -> DataFrame | None:
+        ...
+
     def drop_duplicates(
         self,
         subset: Hashable | Sequence[Hashable] | None = None,