un-comment-out, remove duplicate check

Author: jbrockmendel

pandas/core/indexes/category.py

@@ -22,7 +22,6 @@
 from pandas.core.dtypes.dtypes import CategoricalDtype
 from pandas.core.dtypes.missing import (
     is_valid_na_for_dtype,
-    isna,
 )
 
 from pandas.core.arrays.categorical import (
@@ -272,12 +271,6 @@ def _is_dtype_compat(self, other: Index) -> Categorical:
                 )
             cat = other._values
 
-            if not ((cat == values) | (isna(cat) & isna(values))).all():
-                # GH#37667 see test_equals_non_category
-                raise TypeError(
-                    "categories must match existing categories when appending"
-                )
-
         return cat
 
     def equals(self, other: object) -> bool:

pandas/tests/dtypes/test_dtypes.py

@@ -1,4 +1,5 @@
 import re
+import warnings
 import weakref
 
 import numpy as np
@@ -121,15 +122,17 @@ def test_constructor_invalid(self):
 
     dtype1 = CategoricalDtype(["a", "b"], ordered=True)
     dtype2 = CategoricalDtype(["x", "y"], ordered=False)
-    # c = Categorical([0, 1], dtype=dtype1)
+    with warnings.catch_warnings():
+        warnings.filterwarnings("ignore")
+        c = Categorical([0, 1], dtype=dtype1)
 
     @pytest.mark.parametrize(
         "values, categories, ordered, dtype, expected",
         [
             [None, None, None, None, CategoricalDtype()],
             [None, ["a", "b"], True, None, dtype1],
-            # [c, None, None, dtype2, dtype2],
-            # [c, ["x", "y"], False, None, dtype2],
+            [c, None, None, dtype2, dtype2],
+            [c, ["x", "y"], False, None, dtype2],
         ],
     )
     def test_from_values_or_dtype(self, values, categories, ordered, dtype, expected):