TYP: Add type hint for DataFrame.T and certain array types

Author: qwhelan

doc/source/whatsnew/v1.1.0.rst

@@ -353,6 +353,8 @@ Other
   instead of ``TypeError: Can only append a Series if ignore_index=True or if the Series has a name`` (:issue:`30871`)
 - Set operations on an object-dtype :class:`Index` now always return object-dtype results (:issue:`31401`)
 - Bug in :meth:`AbstractHolidayCalendar.holidays` when no rules were defined (:issue:`31415`)
+- :meth:`DataFrame.T` now has type annotations in line with :meth:`DataFrame.transpose`. Annotations also extended to :class:`Categorical`
+  and :class:`SparseArray` (:issue:`32532`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/arrays/categorical.py

@@ -1317,7 +1317,7 @@ def __setstate__(self, state):
             setattr(self, k, v)
 
     @property
-    def T(self):
+    def T(self) -> "Categorical":
         """
         Return transposed numpy array.
         """

pandas/core/arrays/sparse/array.py

@@ -1296,14 +1296,14 @@ def mean(self, axis=0, *args, **kwargs):
             nsparse = self.sp_index.ngaps
             return (sp_sum + self.fill_value * nsparse) / (ct + nsparse)
 
-    def transpose(self, *axes):
+    def transpose(self, *axes) -> "SparseArray":
         """
         Returns the SparseArray.
         """
         return self
 
     @property
-    def T(self):
+    def T(self) -> "SparseArray":
         """
         Returns the SparseArray.
         """

pandas/core/frame.py

@@ -2443,7 +2443,9 @@ def transpose(self, *args, copy: bool = False) -> "DataFrame":
 
         return result.__finalize__(self)
 
-    T = property(transpose)
+    @property
+    def T(self) -> "DataFrame":
+        return self.transpose()
 
     # ----------------------------------------------------------------------
     # Indexing Methods