BUG: GH23227 Fixed

Author: 5hirish

pandas/core/groupby/groupby.py

@@ -759,7 +759,7 @@ def _try_cast(self, result, obj, numeric_only=False):
         else:
             dtype = obj.dtype
 
-        if is_extension_array_dtype(obj.dtype):
+        if is_extension_array_dtype(dtype):
             # The function can return something of any type, so check
             # if the type is compatible with the calling EA.
             try:

pandas/tests/groupby/test_grouping.py

@@ -283,6 +283,9 @@ def test_groupby_categorical_index_and_columns(self, observed):
         assert_frame_equal(result, expected)
 
     def test_groupby_extension_array(self):
+
+        # GH23227
+        # groupby on an extension array should return the extension array type
         df = pd.DataFrame({'Int': pd.Series([1, 2, 3], dtype='Int64'),
                            'A': [1, 2, 1]})
         result = df.groupby('A').Int.sum()