BUG: DatetimeIndex.shift with non-nano (#56117)

* BUG: DatetimeIndex.shift with non-nano

* BUG: DatetimeIndex.shift with non-nano

Author: jbrockmendel

doc/source/whatsnew/v2.2.0.rst

@@ -447,6 +447,7 @@ Datetimelike
 - Bug in :func:`testing.assert_extension_array_equal` that could use the wrong unit when comparing resolutions (:issue:`55730`)
 - Bug in :func:`to_datetime` and :class:`DatetimeIndex` when passing a list of mixed-string-and-numeric types incorrectly raising (:issue:`55780`)
 - Bug in :func:`to_datetime` and :class:`DatetimeIndex` when passing mixed-type objects with a mix of timezones or mix of timezone-awareness failing to raise ``ValueError`` (:issue:`55693`)
+- Bug in :meth:`DatetimeIndex.shift` with non-nanosecond resolution incorrectly returning with nanosecond resolution (:issue:`56117`)
 - Bug in :meth:`DatetimeIndex.union` returning object dtype for tz-aware indexes with the same timezone but different units (:issue:`55238`)
 - Bug in :meth:`Index.is_monotonic_increasing` and :meth:`Index.is_monotonic_decreasing` always caching :meth:`Index.is_unique` as ``True`` when first value in index is ``NaT`` (:issue:`55755`)
 - Bug in :meth:`Index.view` to a datetime64 dtype with non-supported resolution incorrectly raising (:issue:`55710`)

pandas/core/indexes/datetimelike.py

@@ -518,7 +518,7 @@ def shift(self, periods: int = 1, freq=None) -> Self:
         #  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
+            start=start, end=end, periods=None, freq=self.freq, unit=self.unit
         )
         return type(self)._simple_new(result, name=self.name)
 

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

@@ -20,10 +20,10 @@ class TestDatetimeIndexShift:
     # -------------------------------------------------------------
     # DatetimeIndex.shift is used in integer addition
 
-    def test_dti_shift_tzaware(self, tz_naive_fixture):
+    def test_dti_shift_tzaware(self, tz_naive_fixture, unit):
         # GH#9903
         tz = tz_naive_fixture
-        idx = DatetimeIndex([], name="xxx", tz=tz)
+        idx = DatetimeIndex([], name="xxx", tz=tz).as_unit(unit)
         tm.assert_index_equal(idx.shift(0, freq="h"), idx)
         tm.assert_index_equal(idx.shift(3, freq="h"), idx)
 
@@ -32,50 +32,53 @@ def test_dti_shift_tzaware(self, tz_naive_fixture):
             name="xxx",
             tz=tz,
             freq="h",
-        )
+        ).as_unit(unit)
         tm.assert_index_equal(idx.shift(0, freq="h"), idx)
         exp = DatetimeIndex(
             ["2011-01-01 13:00", "2011-01-01 14:00", "2011-01-01 15:00"],
             name="xxx",
             tz=tz,
             freq="h",
-        )
+        ).as_unit(unit)
         tm.assert_index_equal(idx.shift(3, freq="h"), exp)
         exp = DatetimeIndex(
             ["2011-01-01 07:00", "2011-01-01 08:00", "2011-01-01 09:00"],
             name="xxx",
             tz=tz,
             freq="h",
-        )
+        ).as_unit(unit)
         tm.assert_index_equal(idx.shift(-3, freq="h"), exp)
 
-    def test_dti_shift_freqs(self):
+    def test_dti_shift_freqs(self, unit):
         # test shift for DatetimeIndex and non DatetimeIndex
         # GH#8083
-        drange = date_range("20130101", periods=5)
+        drange = date_range("20130101", periods=5, unit=unit)
         result = drange.shift(1)
         expected = DatetimeIndex(
             ["2013-01-02", "2013-01-03", "2013-01-04", "2013-01-05", "2013-01-06"],
+            dtype=f"M8[{unit}]",
             freq="D",
         )
         tm.assert_index_equal(result, expected)
 
         result = drange.shift(-1)
         expected = DatetimeIndex(
             ["2012-12-31", "2013-01-01", "2013-01-02", "2013-01-03", "2013-01-04"],
+            dtype=f"M8[{unit}]",
             freq="D",
         )
         tm.assert_index_equal(result, expected)
 
         result = drange.shift(3, freq="2D")
         expected = DatetimeIndex(
             ["2013-01-07", "2013-01-08", "2013-01-09", "2013-01-10", "2013-01-11"],
+            dtype=f"M8[{unit}]",
             freq="D",
         )
         tm.assert_index_equal(result, expected)
 
-    def test_dti_shift_int(self):
-        rng = date_range("1/1/2000", periods=20)
+    def test_dti_shift_int(self, unit):
+        rng = date_range("1/1/2000", periods=20, unit=unit)
 
         result = rng + 5 * rng.freq
         expected = rng.shift(5)
@@ -85,25 +88,27 @@ def test_dti_shift_int(self):
         expected = rng.shift(-5)
         tm.assert_index_equal(result, expected)
 
-    def test_dti_shift_no_freq(self):
+    def test_dti_shift_no_freq(self, unit):
         # GH#19147
-        dti = DatetimeIndex(["2011-01-01 10:00", "2011-01-01"], freq=None)
+        dti = DatetimeIndex(["2011-01-01 10:00", "2011-01-01"], freq=None).as_unit(unit)
         with pytest.raises(NullFrequencyError, match="Cannot shift with no freq"):
             dti.shift(2)
 
     @pytest.mark.parametrize("tzstr", ["US/Eastern", "dateutil/US/Eastern"])
-    def test_dti_shift_localized(self, tzstr):
-        dr = date_range("2011/1/1", "2012/1/1", freq="W-FRI")
+    def test_dti_shift_localized(self, tzstr, unit):
+        dr = date_range("2011/1/1", "2012/1/1", freq="W-FRI", unit=unit)
         dr_tz = dr.tz_localize(tzstr)
 
         result = dr_tz.shift(1, "10min")
         assert result.tz == dr_tz.tz
 
-    def test_dti_shift_across_dst(self):
+    def test_dti_shift_across_dst(self, unit):
         # GH 8616
-        idx = date_range("2013-11-03", tz="America/Chicago", periods=7, freq="h")
-        s = Series(index=idx[:-1], dtype=object)
-        result = s.shift(freq="h")
+        idx = date_range(
+            "2013-11-03", tz="America/Chicago", periods=7, freq="h", unit=unit
+        )
+        ser = Series(index=idx[:-1], dtype=object)
+        result = ser.shift(freq="h")
         expected = Series(index=idx[1:], dtype=object)
         tm.assert_series_equal(result, expected)
 
@@ -115,24 +120,26 @@ def test_dti_shift_across_dst(self):
             [1, "2014-11-14 01:00:00"],
         ],
     )
-    def test_dti_shift_near_midnight(self, shift, result_time):
+    def test_dti_shift_near_midnight(self, shift, result_time, unit):
         # GH 8616
         dt = datetime(2014, 11, 14, 0)
         dt_est = pytz.timezone("EST").localize(dt)
-        s = Series(data=[1], index=[dt_est])
-        result = s.shift(shift, freq="h")
-        expected = Series(1, index=DatetimeIndex([result_time], tz="EST"))
+        idx = DatetimeIndex([dt_est]).as_unit(unit)
+        ser = Series(data=[1], index=idx)
+        result = ser.shift(shift, freq="h")
+        exp_index = DatetimeIndex([result_time], tz="EST").as_unit(unit)
+        expected = Series(1, index=exp_index)
         tm.assert_series_equal(result, expected)
 
-    def test_shift_periods(self):
+    def test_shift_periods(self, unit):
         # GH#22458 : argument 'n' was deprecated in favor of 'periods'
-        idx = date_range(start=START, end=END, periods=3)
+        idx = date_range(start=START, end=END, periods=3, unit=unit)
         tm.assert_index_equal(idx.shift(periods=0), idx)
         tm.assert_index_equal(idx.shift(0), idx)
 
     @pytest.mark.parametrize("freq", ["B", "C"])
-    def test_shift_bday(self, freq):
-        rng = date_range(START, END, freq=freq)
+    def test_shift_bday(self, freq, unit):
+        rng = date_range(START, END, freq=freq, unit=unit)
         shifted = rng.shift(5)
         assert shifted[0] == rng[5]
         assert shifted.freq == rng.freq
@@ -145,18 +152,18 @@ def test_shift_bday(self, freq):
         assert shifted[0] == rng[0]
         assert shifted.freq == rng.freq
 
-    def test_shift_bmonth(self):
-        rng = date_range(START, END, freq=pd.offsets.BMonthEnd())
+    def test_shift_bmonth(self, unit):
+        rng = date_range(START, END, freq=pd.offsets.BMonthEnd(), unit=unit)
         shifted = rng.shift(1, freq=pd.offsets.BDay())
         assert shifted[0] == rng[0] + pd.offsets.BDay()
 
-        rng = date_range(START, END, freq=pd.offsets.BMonthEnd())
+        rng = date_range(START, END, freq=pd.offsets.BMonthEnd(), unit=unit)
         with tm.assert_produces_warning(pd.errors.PerformanceWarning):
             shifted = rng.shift(1, freq=pd.offsets.CDay())
             assert shifted[0] == rng[0] + pd.offsets.CDay()
 
-    def test_shift_empty(self):
+    def test_shift_empty(self, unit):
         # GH#14811
-        dti = date_range(start="2016-10-21", end="2016-10-21", freq="BME")
+        dti = date_range(start="2016-10-21", end="2016-10-21", freq="BME", unit=unit)
         result = dti.shift(1)
         tm.assert_index_equal(result, dti)