BUG: Ensure that Index._data is an ndarray

Split from pandas-dev#23623, where it was
causing issues with infer_dtype.

Author: TomAugspurger

pandas/core/indexes/base.py

@@ -523,8 +523,6 @@ def _simple_new(cls, values, name=None, dtype=None, **kwargs):
                                  **kwargs)._ndarray_values
 
         if isinstance(values, (ABCSeries, cls)):
-            # TODO: check this in all the callers. We shouldn't be getting
-            # an Inex here.
             values = np.asarray(values._values)
 
         assert isinstance(values, np.ndarray)

pandas/tests/indexes/test_base.py

@@ -504,6 +504,12 @@ def test_constructor_cast(self):
         with pytest.raises(ValueError, match=msg):
             Index(["a", "b", "c"], dtype=float)
 
+    def test_constructor_unwraps_index(self):
+        a = pd.Index([True, False])
+        b = pd.Index(a)
+        expected = np.array([True, False], dtype=object)
+        tm.assert_numpy_array_equal(b._data, expected)
+
     def test_view_with_args(self):
 
         restricted = ['unicodeIndex', 'strIndex', 'catIndex', 'boolIndex',

pandas/tests/indexes/test_numeric.py

@@ -628,6 +628,12 @@ def test_constructor_coercion_signed_to_unsigned(self, uint_dtype):
         with pytest.raises(OverflowError, match=msg):
             Index([-1], dtype=uint_dtype)
 
+    def test_constructor_unwraps_index(self):
+        idx = pd.Index([1, 2])
+        result = pd.Int64Index(idx)
+        expected = np.array([1, 2], dtype='int64')
+        tm.assert_numpy_array_equal(result._data, expected)
+
     def test_coerce_list(self):
         # coerce things
         arr = Index([1, 2, 3, 4])