BUG/TST/REF: Datetimelike Arithmetic Methods

doc/source/whatsnew/v0.24.0.txt

@@ -825,7 +825,8 @@ Timedelta
 - Bug in :class:`TimedeltaIndex` incorrectly allowing indexing with ``Timestamp`` object (:issue:`20464`)
 - Fixed bug where subtracting :class:`Timedelta` from an object-dtyped array would raise ``TypeError`` (:issue:`21980`)
 - Fixed bug in adding a :class:`DataFrame` with all-`timedelta64[ns]` dtypes to a :class:`DataFrame` with all-integer dtypes returning incorrect results instead of raising ``TypeError`` (:issue:`22696`)
--
+- Bug in :class:`TimedeltaIndex` where adding a timezone-aware datetime scalar incorrectly returned a timezone-naive :class:`DatetimeIndex` (:issue:`23215`)
+- Bug in :class:`TimedeltaIndex` where adding ``np.timedelta64('NaT')`` incorrectly returned an all-`NaT` :class:`DatetimeIndex` instead of an all-`NaT` :class:`TimedeltaIndex` (:issue:`23215`)
 
 Timezones
 ^^^^^^^^^

pandas/core/arrays/datetimelike.py

@@ -246,27 +246,6 @@ def _maybe_mask_results(self, result, fill_value=None, convert=None):
             result[self._isnan] = fill_value
         return result
 
-    def _nat_new(self, box=True):
-        """
-        Return Array/Index or ndarray filled with NaT which has the same
-        length as the caller.
-
-        Parameters
-        ----------
-        box : boolean, default True
-            - If True returns a Array/Index as the same as caller.
-            - If False returns ndarray of np.int64.
-        """
-        result = np.zeros(len(self), dtype=np.int64)
-        result.fill(iNaT)
-        if not box:
-            return result
-
-        attribs = self._get_attributes_dict()
-        if not is_period_dtype(self):
-            attribs['freq'] = None
-        return self._simple_new(result, **attribs)
-
     # ------------------------------------------------------------------
     # Frequency Properties/Methods
 
@@ -347,21 +326,59 @@ def _validate_frequency(cls, index, freq, **kwargs):
     # Arithmetic Methods
 
     def _add_datelike(self, other):
+        # Overriden by TimedeltaArray
         raise TypeError("cannot add {cls} and {typ}"
                         .format(cls=type(self).__name__,
                                 typ=type(other).__name__))
 
+    _add_datelike_dti = _add_datelike
+
     def _sub_datelike(self, other):
-        raise com.AbstractMethodError(self)
+        # Overridden by DatetimeArray
+        assert other is not NaT
+        raise TypeError("cannot subtract a datelike from a {cls}"
+                        .format(cls=type(self).__name__))
+
+    _sub_datelike_dti = _sub_datelike
 
     def _sub_period(self, other):
-        return NotImplemented
+        # Overriden by PeriodArray
+        raise TypeError("cannot subtract Period from a {cls}"
+                        .format(cls=type(self).__name__))
 
     def _add_offset(self, offset):
         raise com.AbstractMethodError(self)
 
     def _add_delta(self, other):
-        return NotImplemented
+        """
+        Add a timedelta-like, DateOffset, or TimedeltaIndex-like object
+        to self.
+
+        Parameters
+        ----------
+        delta : {timedelta, np.timedelta64, DateOffset,
+                 TimedeltaIndex, ndarray[timedelta64]}
+
+        Returns
+        -------
+        result : same type as self
+
+        Notes
+        -----
+        The result's name is set outside of _add_delta by the calling
+        method (__add__ or __sub__), if necessary (i.e. for Indexes).
+        """
+        # Note: The docstring here says the return type is the same type
+        #   as self, which is inaccurate.  Once wrapped by the inheriting
+        #   Array classes, this will be accurate.
+
+        if isinstance(other, (Tick, timedelta, np.timedelta64)):
+            new_values = self._add_delta_td(other)
+        elif is_timedelta64_dtype(other):
+            # ndarray[timedelta64] or TimedeltaArray/index
+            new_values = self._add_delta_tdi(other)
+
+        return new_values
 
     def _add_delta_td(self, other):
         """
@@ -371,16 +388,15 @@ def _add_delta_td(self, other):
         inc = delta_to_nanoseconds(other)
         new_values = checked_add_with_arr(self.asi8, inc,
                                           arr_mask=self._isnan).view('i8')
-        if self.hasnans:
-            new_values[self._isnan] = iNaT
+        new_values = self._maybe_mask_results(new_values, fill_value=iNaT)
         return new_values.view('i8')
 
     def _add_delta_tdi(self, other):
         """
         Add a delta of a TimedeltaIndex
         return the i8 result view
         """
-        if not len(self) == len(other):
+        if len(self) != len(other):
             raise ValueError("cannot add indices of unequal length")
 
         if isinstance(other, np.ndarray):
@@ -407,7 +423,9 @@ def _add_nat(self):
 
         # GH#19124 pd.NaT is treated like a timedelta for both timedelta
         # and datetime dtypes
-        return self._nat_new(box=True)
+        result = np.zeros(len(self), dtype=np.int64)
+        result.fill(iNaT)
+        return self._shallow_copy(result, freq=None)
 
     def _sub_nat(self):
         """Subtract pd.NaT from self"""
@@ -441,7 +459,7 @@ def _sub_period_array(self, other):
                             .format(dtype=other.dtype,
                                     cls=type(self).__name__))
 
-        if not len(self) == len(other):
+        if len(self) != len(other):
             raise ValueError("cannot subtract arrays/indices of "
                              "unequal length")
         if self.freq != other.freq:
@@ -635,7 +653,7 @@ def __add__(self, other):
                 result = self._addsub_offset_array(other, operator.add)
             elif is_datetime64_dtype(other) or is_datetime64tz_dtype(other):
                 # DatetimeIndex, ndarray[datetime64]
-                return self._add_datelike(other)
+                return self._add_datelike_dti(other)
             elif is_integer_dtype(other):
                 result = self._addsub_int_array(other, operator.add)
             elif is_float_dtype(other):
@@ -695,7 +713,7 @@ def __sub__(self, other):
                 result = self._addsub_offset_array(other, operator.sub)
             elif is_datetime64_dtype(other) or is_datetime64tz_dtype(other):
                 # DatetimeIndex, ndarray[datetime64]
-                result = self._sub_datelike(other)
+                result = self._sub_datelike_dti(other)
             elif is_period_dtype(other):
                 # PeriodIndex
                 result = self._sub_period_array(other)

pandas/core/arrays/datetimes.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-from datetime import datetime, timedelta, time
+from datetime import datetime, time
 import warnings
 
 import numpy as np
@@ -12,7 +12,7 @@
     conversion, fields, timezones,
     resolution as libresolution)
 
-from pandas.util._decorators import cache_readonly
+from pandas.util._decorators import cache_readonly, Appender
 from pandas.errors import PerformanceWarning
 from pandas import compat
 
@@ -21,7 +21,6 @@
     is_object_dtype,
     is_datetime64tz_dtype,
     is_datetime64_dtype,
-    is_timedelta64_dtype,
     ensure_int64)
 from pandas.core.dtypes.dtypes import DatetimeTZDtype
 from pandas.core.dtypes.missing import isna
@@ -425,10 +424,20 @@ def _assert_tzawareness_compat(self, other):
     # Arithmetic Methods
 
     def _sub_datelike_dti(self, other):
-        """subtraction of two DatetimeIndexes"""
-        if not len(self) == len(other):
+        """subtract DatetimeArray/Index or ndarray[datetime64]"""
+        if len(self) != len(other):
             raise ValueError("cannot add indices of unequal length")
 
+        if isinstance(other, np.ndarray):
+            # if other is an ndarray, we assume it is datetime64-dtype
+            other = type(self)(other)
+
+        if not self._has_same_tz(other):
+            # require tz compat
+            raise TypeError("{cls} subtraction must have the same "
+                            "timezones or no timezones"
+                            .format(cls=type(self).__name__))
+
         self_i8 = self.asi8
         other_i8 = other.asi8
         new_values = checked_add_with_arr(self_i8, -other_i8,
@@ -458,72 +467,27 @@ def _add_offset(self, offset):
 
     def _sub_datelike(self, other):
         # subtract a datetime from myself, yielding a ndarray[timedelta64[ns]]
-        if isinstance(other, (DatetimeArrayMixin, np.ndarray)):
-            if isinstance(other, np.ndarray):
-                # if other is an ndarray, we assume it is datetime64-dtype
-                other = type(self)(other)
-            if not self._has_same_tz(other):
-                # require tz compat
-                raise TypeError("{cls} subtraction must have the same "
-                                "timezones or no timezones"
-                                .format(cls=type(self).__name__))
-            result = self._sub_datelike_dti(other)
-        elif isinstance(other, (datetime, np.datetime64)):
-            assert other is not NaT
-            other = Timestamp(other)
-            if other is NaT:
-                return self - NaT
+        assert isinstance(other, (datetime, np.datetime64))
+        assert other is not NaT
+        other = Timestamp(other)
+        if other is NaT:
+            return self - NaT
+
+        if not self._has_same_tz(other):
             # require tz compat
-            elif not self._has_same_tz(other):
-                raise TypeError("Timestamp subtraction must have the same "
-                                "timezones or no timezones")
-            else:
-                i8 = self.asi8
-                result = checked_add_with_arr(i8, -other.value,
-                                              arr_mask=self._isnan)
-                result = self._maybe_mask_results(result,
-                                                  fill_value=iNaT)
-        else:
-            raise TypeError("cannot subtract {cls} and {typ}"
-                            .format(cls=type(self).__name__,
-                                    typ=type(other).__name__))
+            raise TypeError("Timestamp subtraction must have the same "
+                            "timezones or no timezones")
+
+        i8 = self.asi8
+        result = checked_add_with_arr(i8, -other.value,
+                                      arr_mask=self._isnan)
+        result = self._maybe_mask_results(result, fill_value=iNaT)
         return result.view('timedelta64[ns]')
 
+    @Appender(dtl.DatetimeLikeArrayMixin._add_delta.__doc__)
     def _add_delta(self, delta):
-        """
-        Add a timedelta-like, DateOffset, or TimedeltaIndex-like object
-        to self.
-
-        Parameters
-        ----------
-        delta : {timedelta, np.timedelta64, DateOffset,
-                 TimedeltaIndex, ndarray[timedelta64]}
-
-        Returns
-        -------
-        result : same type as self
-
-        Notes
-        -----
-        The result's name is set outside of _add_delta by the calling
-        method (__add__ or __sub__)
-        """
-        from pandas.core.arrays import TimedeltaArrayMixin
-
-        if isinstance(delta, (Tick, timedelta, np.timedelta64)):
-            new_values = self._add_delta_td(delta)
-        elif is_timedelta64_dtype(delta):
-            if not isinstance(delta, TimedeltaArrayMixin):
-                delta = TimedeltaArrayMixin(delta)
-            new_values = self._add_delta_tdi(delta)
-        else:
-            new_values = self.astype('O') + delta
-
-        tz = 'UTC' if self.tz is not None else None
-        result = type(self)(new_values, tz=tz, freq='infer')
-        if self.tz is not None and self.tz is not utc:
-            result = result.tz_convert(self.tz)
-        return result
+        new_values = dtl.DatetimeLikeArrayMixin._add_delta(self, delta)
+        return type(self)(new_values, tz=self.tz, freq='infer')
 
     # -----------------------------------------------------------------
     # Timezone Conversion and Localization Methods

pandas/core/arrays/period.py

@@ -15,10 +15,10 @@
 from pandas._libs.tslibs.fields import isleapyear_arr
 
 from pandas import compat
-from pandas.util._decorators import (cache_readonly, deprecate_kwarg)
+from pandas.util._decorators import cache_readonly, deprecate_kwarg, Appender
 
 from pandas.core.dtypes.common import (
-    is_integer_dtype, is_float_dtype, is_period_dtype, is_timedelta64_dtype,
+    is_integer_dtype, is_float_dtype, is_period_dtype,
     is_datetime64_dtype, _TD_DTYPE)
 from pandas.core.dtypes.dtypes import PeriodDtype
 from pandas.core.dtypes.generic import ABCSeries
@@ -334,10 +334,6 @@ def to_timestamp(self, freq=None, how='start'):
 
     _create_comparison_method = classmethod(_period_array_cmp)
 
-    def _sub_datelike(self, other):
-        assert other is not NaT
-        return NotImplemented
-
     def _sub_period(self, other):
         # If the operation is well-defined, we return an object-Index
         # of DateOffsets.  Null entries are filled with pd.NaT
@@ -349,9 +345,7 @@ def _sub_period(self, other):
         new_data = asi8 - other.ordinal
         new_data = np.array([self.freq * x for x in new_data])
 
-        if self.hasnans:
-            new_data[self._isnan] = NaT
-
+        new_data = self._maybe_mask_results(new_data, fill_value=NaT)
         return new_data
 
     def _add_offset(self, other):
@@ -379,38 +373,18 @@ def _add_delta_tdi(self, other):
         delta = self._check_timedeltalike_freq_compat(other)
         return self._addsub_int_array(delta, operator.add)
 
+    @Appender(DatetimeLikeArrayMixin._add_delta.__doc__)
     def _add_delta(self, other):
-        """
-        Add a timedelta-like, Tick, or TimedeltaIndex-like object
-        to self.
-
-        Parameters
-        ----------
-        other : {timedelta, np.timedelta64, Tick,
-                 TimedeltaIndex, ndarray[timedelta64]}
-
-        Returns
-        -------
-        result : same type as self
-        """
         if not isinstance(self.freq, Tick):
             # We cannot add timedelta-like to non-tick PeriodArray
             raise IncompatibleFrequency("Input has different freq from "
                                         "{cls}(freq={freqstr})"
                                         .format(cls=type(self).__name__,
                                                 freqstr=self.freqstr))
 
-        # TODO: standardize across datetimelike subclasses whether to return
-        #  i8 view or _shallow_copy
-        if isinstance(other, (Tick, timedelta, np.timedelta64)):
-            new_values = self._add_delta_td(other)
-            return self._shallow_copy(new_values)
-        elif is_timedelta64_dtype(other):
-            # ndarray[timedelta64] or TimedeltaArray/index
-            new_values = self._add_delta_tdi(other)
-            return self._shallow_copy(new_values)
-        else:  # pragma: no cover
-            raise TypeError(type(other).__name__)
+        new_values = DatetimeLikeArrayMixin._add_delta(self, other)
+
+        return self._shallow_copy(new_values)
 
     @deprecate_kwarg(old_arg_name='n', new_arg_name='periods')
     def shift(self, periods):