Note __pow__ return type (data-apis#182)

* note pow return type

* use dtype

* note int to float return type

* Update spec/API_specification/dataframe_api/dataframe_object.py

Co-authored-by: Keith Kraus <[email protected]>

* Update spec/API_specification/dataframe_api/column_object.py

Co-authored-by: Keith Kraus <[email protected]>

---------

Co-authored-by: Keith Kraus <[email protected]>

Author: MarcoGorelli

spec/API_specification/dataframe_api/column_object.py

@@ -363,6 +363,10 @@ def __pow__(self, other: Column | Scalar) -> Column:
         """
         Raise this column to the power of `other`.
 
+        Integer dtype to the power of non-negative integer dtype is integer dtype.
+        Integer dtype to the power of float dtype is float dtype.
+        Float dtype to the power of integer dtype or float dtype is float dtype.
+
         Parameters
         ----------
         other : Column or Scalar

spec/API_specification/dataframe_api/dataframe_object.py

@@ -528,6 +528,10 @@ def __pow__(self, other: DataFrame | Scalar) -> DataFrame:
         """
         Raise this dataframe to the power of `other`.
 
+        Integer dtype to the power of non-negative integer dtype is integer dtype.
+        Integer dtype to the power of float dtype is float dtype.
+        Float dtype to the power of integer dtype or float dtype is float dtype.
+
         Parameters
         ----------
         other : DataFrame or Scalar