TYP: func argument to DataFrame.apply, DataFrame.applymap, core.apply.frame_apply (pandas-dev#38493)

Author: arw2019

pandas/_typing.py

@@ -133,6 +133,8 @@
     "Resampler",
 ]
 
+PythonFuncType = Callable[[Any], Any]
+
 # filenames and file-like-objects
 Buffer = Union[IO[AnyStr], RawIOBase, BufferedIOBase, TextIOBase, TextIOWrapper, mmap]
 FileOrBuffer = Union[str, Buffer[T]]

pandas/core/apply.py

@@ -6,7 +6,7 @@
 
 from pandas._config import option_context
 
-from pandas._typing import Axis, FrameOrSeriesUnion
+from pandas._typing import AggFuncType, Axis, FrameOrSeriesUnion
 from pandas.util._decorators import cache_readonly
 
 from pandas.core.dtypes.common import (
@@ -27,7 +27,7 @@
 
 def frame_apply(
     obj: "DataFrame",
-    func,
+    func: AggFuncType,
     axis: Axis = 0,
     raw: bool = False,
     result_type: Optional[str] = None,

pandas/core/frame.py

@@ -62,6 +62,7 @@
     IndexLabel,
     Label,
     Level,
+    PythonFuncType,
     Renamer,
     StorageOptions,
     Suffixes,
@@ -7661,7 +7662,13 @@ def transform(
         return result
 
     def apply(
-        self, func, axis: Axis = 0, raw: bool = False, result_type=None, args=(), **kwds
+        self,
+        func: AggFuncType,
+        axis: Axis = 0,
+        raw: bool = False,
+        result_type=None,
+        args=(),
+        **kwds,
     ):
         """
         Apply a function along an axis of the DataFrame.
@@ -7807,7 +7814,9 @@ def apply(
         )
         return op.get_result()
 
-    def applymap(self, func, na_action: Optional[str] = None) -> DataFrame:
+    def applymap(
+        self, func: PythonFuncType, na_action: Optional[str] = None
+    ) -> DataFrame:
         """
         Apply a function to a Dataframe elementwise.