BUG/CLN: datetimelike Index.equals may return True with non-Index

closes #13107

Author: sinhrks <sinhrks@gmail.com>

Closes #13986 from sinhrks/dti_equals and squashes the following commits:

580151a [sinhrks] BUG/CLN: move .equals to DatetimeOpsMixin

doc/source/whatsnew/v0.19.0.txt

@@ -1461,6 +1461,7 @@ Bug Fixes
 - Bug in operations on ``NaT`` returning ``float`` instead of ``datetime64[ns]`` (:issue:`12941`)
 - Bug in ``Series`` flexible arithmetic methods (like ``.add()``) raises ``ValueError`` when ``axis=None`` (:issue:`13894`)
 - Bug in ``DataFrame.to_csv()`` with ``MultiIndex`` columns in which a stray empty line was added (:issue:`6618`)
+- Bug in ``DatetimeIndex``, ``TimedeltaIndex`` and ``PeriodIndex.equals()`` may return ``True`` when input isn't ``Index`` but contains the same values (:issue:`13107`)
 
 
 - Bug in ``Index`` raises ``KeyError`` displaying incorrect column when column is not in the df and columns contains duplicate values (:issue:`13822`)

pandas/indexes/base.py

@@ -1605,8 +1605,15 @@ def equals(self, other):
         if not isinstance(other, Index):
             return False
 
-        return array_equivalent(_values_from_object(self),
-                                _values_from_object(other))
+        if is_object_dtype(self) and not is_object_dtype(other):
+            # if other is not object, use other's logic for coercion
+            return other.equals(self)
+
+        try:
+            return array_equivalent(_values_from_object(self),
+                                    _values_from_object(other))
+        except:
+            return False
 
     def identical(self, other):
         """Similar to equals, but check that other comparable attributes are

pandas/indexes/category.py

@@ -196,6 +196,9 @@ def equals(self, other):
         if self.is_(other):
             return True
 
+        if not isinstance(other, Index):
+            return False
+
         try:
             other = self._is_dtype_compat(other)
             return array_equivalent(self._data, other)

pandas/indexes/multi.py

@@ -1436,6 +1436,7 @@ def reindex(self, target, method=None, level=None, limit=None,
                                                   return_indexers=True,
                                                   keep_order=False)
         else:
+            target = _ensure_index(target)
             if self.equals(target):
                 indexer = None
             else:
@@ -1984,6 +1985,9 @@ def equals(self, other):
         if self.is_(other):
             return True
 
+        if not isinstance(other, Index):
+            return False
+
         if not isinstance(other, MultiIndex):
             return array_equivalent(self._values,
                                     _values_from_object(_ensure_index(other)))

pandas/indexes/numeric.py

@@ -7,7 +7,7 @@
 from pandas.types.common import (is_dtype_equal, pandas_dtype,
                                  is_float_dtype, is_object_dtype,
                                  is_integer_dtype, is_scalar)
-from pandas.types.missing import array_equivalent, isnull
+from pandas.types.missing import isnull
 from pandas.core.common import _values_from_object
 
 from pandas import compat
@@ -160,16 +160,6 @@ def _convert_scalar_indexer(self, key, kind=None):
         return (super(Int64Index, self)
                 ._convert_scalar_indexer(key, kind=kind))
 
-    def equals(self, other):
-        """
-        Determines if two Index objects contain the same elements.
-        """
-        if self.is_(other):
-            return True
-
-        return array_equivalent(_values_from_object(self),
-                                _values_from_object(other))
-
     def _wrap_joined_index(self, joined, other):
         name = self.name if self.name == other.name else None
         return Int64Index(joined, name=name)
@@ -306,6 +296,9 @@ def equals(self, other):
         if self is other:
             return True
 
+        if not isinstance(other, Index):
+            return False
+
         # need to compare nans locations and make sure that they are the same
         # since nans don't compare equal this is a bit tricky
         try:

pandas/tests/indexes/common.py

@@ -650,6 +650,20 @@ def test_delete_base(self):
                 # either depending on numpy version
                 result = idx.delete(len(idx))
 
+    def test_equals(self):
+
+        for name, idx in compat.iteritems(self.indices):
+            self.assertTrue(idx.equals(idx))
+            self.assertTrue(idx.equals(idx.copy()))
+            self.assertTrue(idx.equals(idx.astype(object)))
+
+            self.assertFalse(idx.equals(list(idx)))
+            self.assertFalse(idx.equals(np.array(idx)))
+
+            if idx.nlevels == 1:
+                # do not test MultiIndex
+                self.assertFalse(idx.equals(pd.Series(idx)))
+
     def test_equals_op(self):
         # GH9947, GH10637
         index_a = self.create_index()

pandas/tests/indexes/test_base.py

@@ -400,7 +400,7 @@ def test_astype(self):
         casted = self.intIndex.astype('i8')
         self.assertEqual(casted.name, 'foobar')
 
-    def test_equals(self):
+    def test_equals_object(self):
         # same
         self.assertTrue(Index(['a', 'b', 'c']).equals(Index(['a', 'b', 'c'])))
 

pandas/tests/indexes/test_category.py

@@ -522,7 +522,7 @@ def test_ensure_copied_data(self):
             result = CategoricalIndex(index.values, copy=False)
             self.assertIs(_base(index.values), _base(result.values))
 
-    def test_equals(self):
+    def test_equals_categorical(self):
 
         ci1 = CategoricalIndex(['a', 'b'], categories=['a', 'b'], ordered=True)
         ci2 = CategoricalIndex(['a', 'b'], categories=['a', 'b', 'c'],
@@ -556,19 +556,30 @@ def test_equals(self):
 
         # tests
         # make sure that we are testing for category inclusion properly
-        self.assertTrue(CategoricalIndex(
-            list('aabca'), categories=['c', 'a', 'b']).equals(list('aabca')))
+        ci = CategoricalIndex(list('aabca'), categories=['c', 'a', 'b'])
+        self.assertFalse(ci.equals(list('aabca')))
+        self.assertFalse(ci.equals(CategoricalIndex(list('aabca'))))
+        self.assertTrue(ci.equals(ci.copy()))
+
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            ci = CategoricalIndex(list('aabca'),
+                                  categories=['c', 'a', 'b', np.nan])
+        self.assertFalse(ci.equals(list('aabca')))
+        self.assertFalse(ci.equals(CategoricalIndex(list('aabca'))))
         with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
-            self.assertTrue(CategoricalIndex(
-                list('aabca'), categories=['c', 'a', 'b', np.nan]).equals(list(
-                    'aabca')))
-
-        self.assertFalse(CategoricalIndex(
-            list('aabca') + [np.nan], categories=['c', 'a', 'b']).equals(list(
-                'aabca')))
-        self.assertTrue(CategoricalIndex(
-            list('aabca') + [np.nan], categories=['c', 'a', 'b']).equals(list(
-                'aabca') + [np.nan]))
+            self.assertTrue(ci.equals(ci.copy()))
+
+        ci = CategoricalIndex(list('aabca') + [np.nan],
+                              categories=['c', 'a', 'b'])
+        self.assertFalse(ci.equals(list('aabca')))
+        self.assertFalse(ci.equals(CategoricalIndex(list('aabca'))))
+        self.assertTrue(ci.equals(ci.copy()))
+
+        ci = CategoricalIndex(list('aabca') + [np.nan],
+                              categories=['c', 'a', 'b'])
+        self.assertFalse(ci.equals(list('aabca') + [np.nan]))
+        self.assertFalse(ci.equals(CategoricalIndex(list('aabca') + [np.nan])))
+        self.assertTrue(ci.equals(ci.copy()))
 
     def test_string_categorical_index_repr(self):
         # short

pandas/tests/indexes/test_multi.py

@@ -1266,7 +1266,7 @@ def test_to_hierarchical(self):
     def test_bounds(self):
         self.index._bounds
 
-    def test_equals(self):
+    def test_equals_multi(self):
         self.assertTrue(self.index.equals(self.index))
         self.assertTrue(self.index.equal_levels(self.index))
 

pandas/tests/indexes/test_numeric.py

@@ -265,7 +265,7 @@ def test_astype(self):
             i = Float64Index([0, 1.1, np.NAN])
             self.assertRaises(ValueError, lambda: i.astype(dtype))
 
-    def test_equals(self):
+    def test_equals_numeric(self):
 
         i = Float64Index([1.0, 2.0])
         self.assertTrue(i.equals(i))

pandas/tests/indexes/test_range.py

@@ -337,7 +337,7 @@ def test_is_monotonic(self):
         self.assertTrue(index.is_monotonic_increasing)
         self.assertTrue(index.is_monotonic_decreasing)
 
-    def test_equals(self):
+    def test_equals_range(self):
         equiv_pairs = [(RangeIndex(0, 9, 2), RangeIndex(0, 10, 2)),
                        (RangeIndex(0), RangeIndex(1, -1, 3)),
                        (RangeIndex(1, 2, 3), RangeIndex(1, 3, 4)),

pandas/tseries/base.py

@@ -11,7 +11,7 @@
 import numpy as np
 from pandas.types.common import (is_integer, is_float,
                                  is_bool_dtype, _ensure_int64,
-                                 is_scalar,
+                                 is_scalar, is_dtype_equal,
                                  is_list_like)
 from pandas.types.generic import (ABCIndex, ABCSeries,
                                   ABCPeriodIndex, ABCIndexClass)
@@ -109,6 +109,34 @@ def ceil(self, freq):
 class DatetimeIndexOpsMixin(object):
     """ common ops mixin to support a unified inteface datetimelike Index """
 
+    def equals(self, other):
+        """
+        Determines if two Index objects contain the same elements.
+        """
+        if self.is_(other):
+            return True
+
+        if not isinstance(other, ABCIndexClass):
+            return False
+        elif not isinstance(other, type(self)):
+            try:
+                other = type(self)(other)
+            except:
+                return False
+
+        if not is_dtype_equal(self.dtype, other.dtype):
+            # have different timezone
+            return False
+
+        # ToDo: Remove this when PeriodDtype is added
+        elif isinstance(self, ABCPeriodIndex):
+            if not isinstance(other, ABCPeriodIndex):
+                return False
+            if self.freq != other.freq:
+                return False
+
+        return np.array_equal(self.asi8, other.asi8)
+
     def __iter__(self):
         return (self._box_func(v) for v in self.asi8)
 

pandas/tseries/index.py

@@ -1625,26 +1625,6 @@ def is_normalized(self):
     def _resolution(self):
         return period.resolution(self.asi8, self.tz)
 
-    def equals(self, other):
-        """
-        Determines if two Index objects contain the same elements.
-        """
-        if self.is_(other):
-            return True
-
-        if (not hasattr(other, 'inferred_type') or
-                other.inferred_type != 'datetime64'):
-            if self.offset is not None:
-                return False
-            try:
-                other = DatetimeIndex(other)
-            except:
-                return False
-
-        if self._has_same_tz(other):
-            return np.array_equal(self.asi8, other.asi8)
-        return False
-
     def insert(self, loc, item):
         """
         Make new Index inserting new item at location

pandas/tseries/period.py

@@ -596,21 +596,6 @@ def _mpl_repr(self):
         # how to represent ourselves to matplotlib
         return self.asobject.values
 
-    def equals(self, other):
-        """
-        Determines if two Index objects contain the same elements.
-        """
-        if self.is_(other):
-            return True
-
-        if not isinstance(other, PeriodIndex):
-            try:
-                other = PeriodIndex(other)
-            except:
-                return False
-
-        return np.array_equal(self.asi8, other.asi8)
-
     def to_timestamp(self, freq=None, how='start'):
         """
         Cast to DatetimeIndex

pandas/tseries/tdi.py

@@ -806,22 +806,6 @@ def dtype(self):
     def is_all_dates(self):
         return True
 
-    def equals(self, other):
-        """
-        Determines if two Index objects contain the same elements.
-        """
-        if self.is_(other):
-            return True
-
-        if (not hasattr(other, 'inferred_type') or
-                other.inferred_type != 'timedelta64'):
-            try:
-                other = TimedeltaIndex(other)
-            except:
-                return False
-
-        return np.array_equal(self.asi8, other.asi8)
-
     def insert(self, loc, item):
         """
         Make new Index inserting new item at location