BUG: Fix is_categorical_dtype for Sparse[category]

doc/source/whatsnew/v1.2.0.rst

@@ -236,7 +236,7 @@ Bug fixes
 Categorical
 ^^^^^^^^^^^
 
--
+- Bug in :func:`pandas.dtypes.is_categorical_dtype` where sparse categorical dtypes would return ``False`` (:issue:`35793`)
 -
 
 Datetimelike

pandas/core/dtypes/base.py

@@ -287,6 +287,10 @@ def is_dtype(cls, dtype: object) -> bool:
             return False
         elif isinstance(dtype, cls):
             return True
+        elif hasattr(dtype, "subtype") and isinstance(
+            dtype.subtype, cls  # type: ignore[attr-defined]
+        ):
+            return True
         if isinstance(dtype, str):
             try:
                 return cls.construct_from_string(dtype) is not None

pandas/core/dtypes/common.py

@@ -558,8 +558,10 @@ def is_categorical_dtype(arr_or_dtype) -> bool:
     """
     if isinstance(arr_or_dtype, ExtensionDtype):
         # GH#33400 fastpath for dtype object
-        return arr_or_dtype.name == "category"
-
+        return ("category" == arr_or_dtype.name) or (
+            is_sparse(arr_or_dtype)
+            and arr_or_dtype.subtype.name == "category"  # type: ignore[attr-defined]
+        )
     if arr_or_dtype is None:
         return False
     return CategoricalDtype.is_dtype(arr_or_dtype)

pandas/tests/dtypes/test_common.py

@@ -213,6 +213,15 @@ def test_is_categorical_deprecation():
         com.is_categorical([1, 2, 3])
 
 
+def test_is_categorical_sparse_categorical():
+    # https://github.com/pandas-dev/pandas/issues/35793
+    s = pd.Series(
+        ["a", "b", "c"], dtype=pd.SparseDtype(CategoricalDtype(["a", "b", "c"]))
+    )
+    assert com.is_categorical_dtype(s)
+    assert com.is_categorical_dtype(s.dtype)
+
+
 def test_is_datetime64_dtype():
     assert not com.is_datetime64_dtype(object)
     assert not com.is_datetime64_dtype([1, 2, 3])