Fix select_dtypes to work when non-class dtypes present in dataframe (

#8849)

Addresses bug #6919. `issubclass` expects a class, but a list is not a class, so we must add a check  before calling `issubclass` on it.

Authors:
  - Sarah Yurick (https://github.com/sarahyurick)

Approvers:
  - Ashwin Srinath (https://github.com/shwina)
  - GALI PREM SAGAR (https://github.com/galipremsagar)

URL: #8849

python/cudf/cudf/core/dataframe.py

@@ -7359,8 +7359,9 @@ def select_dtypes(self, include=None, exclude=None):
                 # category handling
                 if is_categorical_dtype(i_dtype):
                     include_subtypes.add(i_dtype)
-                elif issubclass(dtype.type, i_dtype):
-                    include_subtypes.add(dtype.type)
+                elif inspect.isclass(dtype.type):
+                    if issubclass(dtype.type, i_dtype):
+                        include_subtypes.add(dtype.type)
 
         # exclude all subtypes
         exclude_subtypes = set()
@@ -7369,8 +7370,9 @@ def select_dtypes(self, include=None, exclude=None):
                 # category handling
                 if is_categorical_dtype(e_dtype):
                     exclude_subtypes.add(e_dtype)
-                elif issubclass(dtype.type, e_dtype):
-                    exclude_subtypes.add(dtype.type)
+                elif inspect.isclass(dtype.type):
+                    if issubclass(dtype.type, e_dtype):
+                        exclude_subtypes.add(dtype.type)
 
         include_all = set(
             [cudf_dtype_from_pydata_dtype(d) for d in self.dtypes]

python/cudf/cudf/tests/test_dataframe.py

@@ -3079,6 +3079,14 @@ def test_select_dtype():
         gdf.select_dtypes(include=["int"], exclude=["object"]),
     )
 
+    gdf = cudf.DataFrame(
+        {"int_col": [0, 1, 2], "list_col": [[1, 2], [3, 4], [5, 6]]}
+    )
+    pdf = gdf.to_pandas()
+    assert_eq(
+        pdf.select_dtypes("int64"), gdf.select_dtypes("int64"),
+    )
+
 
 def test_select_dtype_datetime():
     gdf = cudf.datasets.timeseries(