BUG-24408 Series.dt does not maintain own copy of index

doc/source/whatsnew/v0.24.0.rst

@@ -1321,6 +1321,7 @@ Datetimelike
 - Bug in :class:`DatetimeIndex` and :class:`TimedeltaIndex` where indexing with ``Ellipsis`` would incorrectly lose the index's ``freq`` attribute (:issue:`21282`)
 - Clarified error message produced when passing an incorrect ``freq`` argument to :class:`DatetimeIndex` with ``NaT`` as the first entry in the passed data (:issue:`11587`)
 - Bug in :func:`to_datetime` where ``box`` and ``utc`` arguments were ignored when passing a :class:`DataFrame` or ``dict`` of unit mappings (:issue:`23760`)
+- Bug in :attr:`Series.dt`` where the cache would not update properly after an in-place operation (:issue:`24408`)
 
 Timedelta
 ^^^^^^^^^

pandas/core/indexes/accessors.py

@@ -27,7 +27,6 @@ def __init__(self, data, orig):
         self._parent = data
         self.orig = orig
         self.name = getattr(data, 'name', None)
-        self.index = getattr(data, 'index', None)
         self._freeze()
 
     def _get_values(self):
@@ -71,8 +70,7 @@ def _delegate_property_get(self, name):
             result = take_1d(result, self.orig.cat.codes)
             index = self.orig.index
         else:
-            index = self.index
-
+            index = self._parent.index
         # return the result as a Series, which is by definition a copy
         result = Series(result, index=index, name=self.name)
 
@@ -98,7 +96,7 @@ def _delegate_method(self, name, *args, **kwargs):
         if not is_list_like(result):
             return result
 
-        result = Series(result, index=self.index, name=self.name)
+        result = Series(result, index=self._parent.index, name=self.name)
 
         # setting this object will show a SettingWithCopyWarning/Error
         result._is_copy = ("modifications to a method of a datetimelike "
@@ -261,7 +259,7 @@ def components(self):
         3     0      0        0        3             0             0            0
         4     0      0        0        4             0             0            0
         """  # noqa: E501
-        return self._get_values().components.set_index(self.index)
+        return self._get_values().components.set_index(self._parent.index)
 
     @property
     def freq(self):

pandas/tests/series/test_datetime_values.py

@@ -485,6 +485,13 @@ def test_dt_accessor_invalid(self, ser):
             ser.dt
         assert not hasattr(ser, 'dt')
 
+    def test_dt_accessor_updates_on_inplace(self):
+        s = Series(pd.date_range('2018-01-01', periods=10))
+        s[2] = None
+        s.fillna(pd.Timestamp('2018-01-01'), inplace=True)
+        result = s.dt.date
+        assert result[0] == result[2]
+
     def test_between(self):
         s = Series(bdate_range('1/1/2000', periods=20).astype(object))
         s[::2] = np.nan