BUG: Make DateTimeIndex copy datetime64[ns] data on copy=True

Author: toobaz

pandas/indexes/base.py

@@ -376,6 +376,33 @@ def _shallow_copy_with_infer(self, values=None, **kwargs):
                 pass
         return Index(values, **attributes)
 
+    def _deepcopy_if_needed(self, orig, copy=False):
+        """
+        .. versionadded:: 0.18.2
+
+        Make a copy of self if data coincides (in memory) with orig.
+        Subclasses should override this if self._base is not an ndarray.
+
+        Parameters
+        ----------
+        orig : ndarray
+            other ndarray to compare self._data against
+        copy : boolean, default False
+            when False, do not run any check, just return self
+
+        Returns
+        -------
+        A copy of self if needed, otherwise self : Index
+        """
+        if copy:
+            # Retrieve the "base objects", i.e. the original memory allocations
+            orig = orig if orig.base is None else orig.base
+            new = self._data if self._data.base is None else self._data.base
+            if orig is new:
+                return self.copy(deep=True)
+
+        return self
+
     def _update_inplace(self, result, **kwargs):
         # guard when called from IndexOpsMixin
         raise TypeError("Index can't be updated inplace")

pandas/tseries/index.py

@@ -225,6 +225,12 @@ def __new__(cls, data=None,
                 verify_integrity=True, normalize=False,
                 closed=None, ambiguous='raise', dtype=None, **kwargs):
 
+        # This allows to later ensure that the 'copy' parameter is honored:
+        if isinstance(data, Index):
+            ref_to_data = data._data
+        else:
+            ref_to_data = data
+
         if name is None and hasattr(data, 'name'):
             name = data.name
 
@@ -305,7 +311,7 @@ def __new__(cls, data=None,
                             raise TypeError("Already tz-aware, use tz_convert "
                                             "to convert.")
 
-                    return data
+                    return data._deepcopy_if_needed(ref_to_data, copy)
 
         if issubclass(data.dtype.type, compat.string_types):
             data = tslib.parse_str_array_to_datetime(data, freq=freq,
@@ -338,10 +344,7 @@ def __new__(cls, data=None,
         elif data.dtype == _INT64_DTYPE:
             if isinstance(data, Int64Index):
                 raise TypeError('cannot convert Int64Index->DatetimeIndex')
-            if copy:
-                subarr = np.asarray(data, dtype=_NS_DTYPE)
-            else:
-                subarr = data.view(_NS_DTYPE)
+            subarr = data.view(_NS_DTYPE)
         else:
             if isinstance(data, (ABCSeries, Index)):
                 values = data._values
@@ -417,7 +420,7 @@ def __new__(cls, data=None,
             if inferred:
                 subarr.offset = to_offset(inferred)
 
-        return subarr
+        return subarr._deepcopy_if_needed(ref_to_data, copy)
 
     @classmethod
     def _generate(cls, start, end, periods, name, offset,