REF: remove _time_shift (pandas-dev#49882)

Author: jbrockmendel

pandas/core/arrays/datetimelike.py

@@ -70,7 +70,6 @@
 from pandas.errors import (
     AbstractMethodError,
     InvalidComparison,
-    NullFrequencyError,
     PerformanceWarning,
 )
 from pandas.util._decorators import (
@@ -1360,44 +1359,6 @@ def _addsub_object_array(self, other: np.ndarray, op):
         result = result.reshape(self.shape)
         return result
 
-    def _time_shift(
-        self: DatetimeLikeArrayT, periods: int, freq=None
-    ) -> DatetimeLikeArrayT:
-        """
-        Shift each value by `periods`.
-
-        Note this is different from ExtensionArray.shift, which
-        shifts the *position* of each element, padding the end with
-        missing values.
-
-        Parameters
-        ----------
-        periods : int
-            Number of periods to shift by.
-        freq : pandas.DateOffset, pandas.Timedelta, or str
-            Frequency increment to shift by.
-        """
-        if freq is not None and freq != self.freq:
-            if isinstance(freq, str):
-                freq = to_offset(freq)
-            offset = periods * freq
-            return self + offset
-
-        if periods == 0 or len(self) == 0:
-            # GH#14811 empty case
-            return self.copy()
-
-        if self.freq is None:
-            raise NullFrequencyError("Cannot shift with no freq")
-
-        start = self[0] + periods * self.freq
-        end = self[-1] + periods * self.freq
-
-        # Note: in the DatetimeTZ case, _generate_range will infer the
-        #  appropriate timezone from `start` and `end`, so tz does not need
-        #  to be passed explicitly.
-        return self._generate_range(start=start, end=end, periods=None, freq=self.freq)
-
     @unpack_zerodim_and_defer("__add__")
     def __add__(self, other):
         other_dtype = getattr(other, "dtype", None)

pandas/core/arrays/period.py

@@ -538,28 +538,6 @@ def to_timestamp(self, freq=None, how: str = "start") -> DatetimeArray:
 
     # --------------------------------------------------------------------
 
-    def _time_shift(self, periods: int, freq=None) -> PeriodArray:
-        """
-        Shift each value by `periods`.
-
-        Note this is different from ExtensionArray.shift, which
-        shifts the *position* of each element, padding the end with
-        missing values.
-
-        Parameters
-        ----------
-        periods : int
-            Number of periods to shift by.
-        freq : pandas.DateOffset, pandas.Timedelta, or str
-            Frequency increment to shift by.
-        """
-        if freq is not None:
-            raise TypeError(
-                "`freq` argument is not supported for "
-                f"{type(self).__name__}._time_shift"
-            )
-        return self + periods
-
     def _box_func(self, x) -> Period | NaTType:
         return Period._from_ordinal(ordinal=x, freq=self.freq)
 
@@ -726,8 +704,7 @@ def _addsub_int_array_or_scalar(
         self, other: np.ndarray | int, op: Callable[[Any, Any], Any]
     ) -> PeriodArray:
         """
-        Add or subtract array of integers; equivalent to applying
-        `_time_shift` pointwise.
+        Add or subtract array of integers.
 
         Parameters
         ----------

pandas/core/indexes/datetimelike.py

@@ -33,6 +33,7 @@
     npt,
 )
 from pandas.compat.numpy import function as nv
+from pandas.errors import NullFrequencyError
 from pandas.util._decorators import (
     Appender,
     cache_readonly,
@@ -353,10 +354,7 @@ def shift(self: _T, periods: int = 1, freq=None) -> _T:
         Index.shift : Shift values of Index.
         PeriodIndex.shift : Shift values of PeriodIndex.
         """
-        arr = self._data.view()
-        arr._freq = self.freq
-        result = arr._time_shift(periods, freq=freq)
-        return type(self)._simple_new(result, name=self.name)
+        raise NotImplementedError
 
     # --------------------------------------------------------------------
 
@@ -400,6 +398,32 @@ def values(self) -> np.ndarray:
         # NB: For Datetime64TZ this is lossy
         return self._data._ndarray
 
+    @doc(DatetimeIndexOpsMixin.shift)
+    def shift(self: _TDT, periods: int = 1, freq=None) -> _TDT:
+        if freq is not None and freq != self.freq:
+            if isinstance(freq, str):
+                freq = to_offset(freq)
+            offset = periods * freq
+            return self + offset
+
+        if periods == 0 or len(self) == 0:
+            # GH#14811 empty case
+            return self.copy()
+
+        if self.freq is None:
+            raise NullFrequencyError("Cannot shift with no freq")
+
+        start = self[0] + periods * self.freq
+        end = self[-1] + periods * self.freq
+
+        # Note: in the DatetimeTZ case, _generate_range will infer the
+        #  appropriate timezone from `start` and `end`, so tz does not need
+        #  to be passed explicitly.
+        result = self._data._generate_range(
+            start=start, end=end, periods=None, freq=self.freq
+        )
+        return type(self)._simple_new(result, name=self.name)
+
     # --------------------------------------------------------------------
     # Set Operation Methods
 

pandas/core/indexes/period.py

@@ -481,6 +481,14 @@ def _parsed_string_to_bounds(self, reso: Resolution, parsed: datetime):
         iv = Period(parsed, freq=reso.attr_abbrev)
         return (iv.asfreq(self.freq, how="start"), iv.asfreq(self.freq, how="end"))
 
+    @doc(DatetimeIndexOpsMixin.shift)
+    def shift(self, periods: int = 1, freq=None):
+        if freq is not None:
+            raise TypeError(
+                f"`freq` argument is not supported for {type(self).__name__}.shift"
+            )
+        return self + periods
+
 
 def period_range(
     start=None, end=None, periods: int | None = None, freq=None, name=None

pandas/tests/indexes/period/methods/test_shift.py

@@ -66,7 +66,7 @@ def test_shift_corner_cases(self):
         # GH#9903
         idx = PeriodIndex([], name="xxx", freq="H")
 
-        msg = "`freq` argument is not supported for PeriodArray._time_shift"
+        msg = "`freq` argument is not supported for PeriodIndex.shift"
         with pytest.raises(TypeError, match=msg):
             # period shift doesn't accept freq
             idx.shift(1, freq="H")