From c39abff87e30e334918143b28a13e2d4859fc79d Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Thu, 9 Jun 2022 16:35:07 -0700
Subject: [PATCH 1/2] ENH: support reso in DTA._box_func

---
 pandas/_libs/tslibs/conversion.pxd            |  7 ++-
 pandas/_libs/tslibs/conversion.pyx            | 17 +++++---
 pandas/_libs/tslibs/timestamps.pyx            | 23 ++++++++--
 pandas/_libs/tslibs/tzconversion.pyx          | 13 +++---
 pandas/_libs/tslibs/vectorized.pyx            |  4 +-
 pandas/core/arrays/datetimes.py               |  4 +-
 pandas/tests/arrays/test_datetimes.py         | 43 ++++++++++++++-----
 .../tests/scalar/timestamp/test_timestamp.py  |  6 ++-
 8 files changed, 84 insertions(+), 33 deletions(-)

diff --git a/pandas/_libs/tslibs/conversion.pxd b/pandas/_libs/tslibs/conversion.pxd
index ba03de6f0b81f..fb0c7d71ad58f 100644
--- a/pandas/_libs/tslibs/conversion.pxd
+++ b/pandas/_libs/tslibs/conversion.pxd
@@ -8,7 +8,10 @@ from numpy cimport (
     ndarray,
 )
 
-from pandas._libs.tslibs.np_datetime cimport npy_datetimestruct
+from pandas._libs.tslibs.np_datetime cimport (
+    NPY_DATETIMEUNIT,
+    npy_datetimestruct,
+)
 
 
 cdef class _TSObject:
@@ -31,3 +34,5 @@ cdef int64_t get_datetime64_nanos(object val) except? -1
 cpdef datetime localize_pydatetime(datetime dt, tzinfo tz)
 cdef int64_t cast_from_unit(object ts, str unit) except? -1
 cpdef (int64_t, int) precision_from_unit(str unit)
+
+cdef maybe_localize_tso(_TSObject obj, tzinfo tz, NPY_DATETIMEUNIT reso)
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 57bccd662e1a0..4e1fcbbcdcc61 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -296,14 +296,18 @@ cdef _TSObject convert_to_tsobject(object ts, tzinfo tz, str unit,
         raise TypeError(f'Cannot convert input [{ts}] of type {type(ts)} to '
                         f'Timestamp')
 
+    maybe_localize_tso(obj, tz, NPY_FR_ns)
+    return obj
+
+
+cdef maybe_localize_tso(_TSObject obj, tzinfo tz, NPY_DATETIMEUNIT reso):
     if tz is not None:
-        _localize_tso(obj, tz)
+        _localize_tso(obj, tz, reso)
 
     if obj.value != NPY_NAT:
         # check_overflows needs to run after _localize_tso
-        check_dts_bounds(&obj.dts)
+        check_dts_bounds(&obj.dts, reso)
         check_overflows(obj)
-    return obj
 
 
 cdef _TSObject convert_datetime_to_tsobject(datetime ts, tzinfo tz,
@@ -548,7 +552,7 @@ cdef inline check_overflows(_TSObject obj):
 # ----------------------------------------------------------------------
 # Localization
 
-cdef inline void _localize_tso(_TSObject obj, tzinfo tz):
+cdef inline void _localize_tso(_TSObject obj, tzinfo tz, NPY_DATETIMEUNIT reso):
     """
     Given the UTC nanosecond timestamp in obj.value, find the wall-clock
     representation of that timestamp in the given timezone.
@@ -557,6 +561,7 @@ cdef inline void _localize_tso(_TSObject obj, tzinfo tz):
     ----------
     obj : _TSObject
     tz : tzinfo
+    reso : NPY_DATETIMEUNIT
 
     Returns
     -------
@@ -569,7 +574,7 @@ cdef inline void _localize_tso(_TSObject obj, tzinfo tz):
     cdef:
         int64_t local_val
         Py_ssize_t outpos = -1
-        Localizer info = Localizer(tz, NPY_FR_ns)
+        Localizer info = Localizer(tz, reso)
 
     assert obj.tzinfo is None
 
@@ -584,7 +589,7 @@ cdef inline void _localize_tso(_TSObject obj, tzinfo tz):
             # infer we went through a pytz path, will have outpos!=-1
             tz = tz._tzinfos[tz._transition_info[outpos]]
 
-        dt64_to_dtstruct(local_val, &obj.dts)
+        pandas_datetime_to_datetimestruct(local_val, reso, &obj.dts)
 
     obj.tzinfo = tz
 
diff --git a/pandas/_libs/tslibs/timestamps.pyx b/pandas/_libs/tslibs/timestamps.pyx
index 251211ea61651..c6bae70d04a98 100644
--- a/pandas/_libs/tslibs/timestamps.pyx
+++ b/pandas/_libs/tslibs/timestamps.pyx
@@ -51,6 +51,7 @@ from pandas._libs.tslibs.conversion cimport (
     _TSObject,
     convert_datetime_to_tsobject,
     convert_to_tsobject,
+    maybe_localize_tso,
 )
 from pandas._libs.tslibs.dtypes cimport (
     npy_unit_to_abbrev,
@@ -210,6 +211,23 @@ cdef class _Timestamp(ABCTimestamp):
     # -----------------------------------------------------------------
     # Constructors
 
+    @classmethod
+    def _from_value_and_reso(cls, int64_t value, NPY_DATETIMEUNIT reso, tzinfo tz):
+        cdef:
+            npy_datetimestruct dts
+            _TSObject obj = _TSObject()
+
+        if value == NPY_NAT:
+            return NaT
+
+        obj.value = value
+        pandas_datetime_to_datetimestruct(value, reso, &obj.dts)
+        maybe_localize_tso(obj, tz, reso)
+
+        return create_timestamp_from_ts(
+            value, obj.dts, tz=obj.tzinfo, freq=None, fold=obj.fold, reso=reso
+        )
+
     @classmethod
     def _from_dt64(cls, dt64: np.datetime64):
         # construct a Timestamp from a np.datetime64 object, keeping the
@@ -223,10 +241,7 @@ cdef class _Timestamp(ABCTimestamp):
 
         reso = get_datetime64_unit(dt64)
         value = get_datetime64_value(dt64)
-        pandas_datetime_to_datetimestruct(value, reso, &dts)
-        return create_timestamp_from_ts(
-            value, dts, tz=None, freq=None, fold=0, reso=reso
-        )
+        return cls._from_value_and_reso(value, reso, None)
 
     # -----------------------------------------------------------------
 
diff --git a/pandas/_libs/tslibs/tzconversion.pyx b/pandas/_libs/tslibs/tzconversion.pyx
index 86cda289c80e6..7657633c7215a 100644
--- a/pandas/_libs/tslibs/tzconversion.pyx
+++ b/pandas/_libs/tslibs/tzconversion.pyx
@@ -88,15 +88,16 @@ cdef class Localizer:
                 # NB: using floordiv here is implicitly assuming we will
                 #  never see trans or deltas that are not an integer number
                 #  of seconds.
+                # TODO: avoid these np.array calls
                 if reso == NPY_DATETIMEUNIT.NPY_FR_us:
-                    trans = trans // 1_000
-                    deltas = deltas // 1_000
+                    trans = np.array(trans) // 1_000
+                    deltas = np.array(deltas) // 1_000
                 elif reso == NPY_DATETIMEUNIT.NPY_FR_ms:
-                    trans = trans // 1_000_000
-                    deltas = deltas // 1_000_000
+                    trans = np.array(trans) // 1_000_000
+                    deltas = np.array(deltas) // 1_000_000
                 elif reso == NPY_DATETIMEUNIT.NPY_FR_s:
-                    trans = trans // 1_000_000_000
-                    deltas = deltas // 1_000_000_000
+                    trans = np.array(trans) // 1_000_000_000
+                    deltas = np.array(deltas) // 1_000_000_000
                 else:
                     raise NotImplementedError(reso)
 
diff --git a/pandas/_libs/tslibs/vectorized.pyx b/pandas/_libs/tslibs/vectorized.pyx
index a52823681def6..2cab55e607f15 100644
--- a/pandas/_libs/tslibs/vectorized.pyx
+++ b/pandas/_libs/tslibs/vectorized.pyx
@@ -43,7 +43,7 @@ from .tzconversion cimport Localizer
 
 @cython.boundscheck(False)
 @cython.wraparound(False)
-def tz_convert_from_utc(ndarray stamps, tzinfo tz):
+def tz_convert_from_utc(ndarray stamps, tzinfo tz, NPY_DATETIMEUNIT reso=NPY_FR_ns):
     # stamps is int64_t, arbitrary ndim
     """
     Convert the values (in i8) from UTC to tz
@@ -58,7 +58,7 @@ def tz_convert_from_utc(ndarray stamps, tzinfo tz):
     ndarray[int64]
     """
     cdef:
-        Localizer info = Localizer(tz, reso=NPY_FR_ns)
+        Localizer info = Localizer(tz, reso=reso)
         int64_t utc_val, local_val
         Py_ssize_t pos, i, n = stamps.size
 
diff --git a/pandas/core/arrays/datetimes.py b/pandas/core/arrays/datetimes.py
index da5542feaea56..400958449d3ff 100644
--- a/pandas/core/arrays/datetimes.py
+++ b/pandas/core/arrays/datetimes.py
@@ -546,7 +546,7 @@ def _check_compatible_with(self, other, setitem: bool = False):
     def _box_func(self, x: np.datetime64) -> Timestamp | NaTType:
         # GH#42228
         value = x.view("i8")
-        ts = Timestamp(value, tz=self.tz)
+        ts = Timestamp._from_value_and_reso(value, reso=self._reso, tz=self.tz)
         # Non-overlapping identity check (left operand type: "Timestamp",
         # right operand type: "NaTType")
         if ts is not NaT:  # type: ignore[comparison-overlap]
@@ -775,7 +775,7 @@ def _local_timestamps(self) -> npt.NDArray[np.int64]:
         if self.tz is None or timezones.is_utc(self.tz):
             # Avoid the copy that would be made in tzconversion
             return self.asi8
-        return tz_convert_from_utc(self.asi8, self.tz)
+        return tz_convert_from_utc(self.asi8, self.tz, reso=self._reso)
 
     def tz_convert(self, tz) -> DatetimeArray:
         """
diff --git a/pandas/tests/arrays/test_datetimes.py b/pandas/tests/arrays/test_datetimes.py
index 14d33ee52aae2..03703dfd2eb28 100644
--- a/pandas/tests/arrays/test_datetimes.py
+++ b/pandas/tests/arrays/test_datetimes.py
@@ -4,6 +4,9 @@
 import numpy as np
 import pytest
 
+from pandas._libs.tslibs import tz_compare
+from pandas._libs.tslibs.dtypes import NpyDatetimeUnit
+
 from pandas.core.dtypes.dtypes import DatetimeTZDtype
 
 import pandas as pd
@@ -20,16 +23,28 @@ def unit(self, request):
     @pytest.fixture
     def reso(self, unit):
         """Fixture returning datetime resolution for a given time unit"""
-        # TODO: avoid hard-coding
-        return {"s": 7, "ms": 8, "us": 9}[unit]
+        return {
+            "s": NpyDatetimeUnit.NPY_FR_s.value,
+            "ms": NpyDatetimeUnit.NPY_FR_ms.value,
+            "us": NpyDatetimeUnit.NPY_FR_us.value,
+        }[unit]
+
+    @pytest.fixture
+    def dtype(self, unit, tz_naive_fixture):
+        tz = tz_naive_fixture
+        if tz is None:
+            return np.dtype(f"datetime64[{unit}]")
+        else:
+            return DatetimeTZDtype(unit=unit, tz=tz)
 
-    @pytest.mark.xfail(reason="_box_func is not yet patched to get reso right")
-    def test_non_nano(self, unit, reso):
+    def test_non_nano(self, unit, reso, dtype):
         arr = np.arange(5, dtype=np.int64).view(f"M8[{unit}]")
-        dta = DatetimeArray._simple_new(arr, dtype=arr.dtype)
+        dta = DatetimeArray._simple_new(arr, dtype=dtype)
 
-        assert dta.dtype == arr.dtype
+        assert dta.dtype == dtype
         assert dta[0]._reso == reso
+        assert tz_compare(dta.tz, dta[0].tz)
+        assert (dta[0] == dta[:1]).all()
 
     @pytest.mark.filterwarnings(
         "ignore:weekofyear and week have been deprecated:FutureWarning"
@@ -37,11 +52,19 @@ def test_non_nano(self, unit, reso):
     @pytest.mark.parametrize(
         "field", DatetimeArray._field_ops + DatetimeArray._bool_ops
     )
-    def test_fields(self, unit, reso, field):
-        dti = pd.date_range("2016-01-01", periods=55, freq="D")
-        arr = np.asarray(dti).astype(f"M8[{unit}]")
+    def test_fields(self, unit, reso, field, dtype):
+        tz = getattr(dtype, "tz", None)
+        dti = pd.date_range("2016-01-01", periods=55, freq="D", tz=tz)
+        if tz is None:
+            arr = np.asarray(dti).astype(f"M8[{unit}]")
+        else:
+            arr = np.asarray(dti.tz_convert("UTC").tz_localize(None)).astype(
+                f"M8[{unit}]"
+            )
 
-        dta = DatetimeArray._simple_new(arr, dtype=arr.dtype)
+        dta = DatetimeArray._simple_new(arr, dtype=dtype)
+
+        # FIXME: assert (dti == dta).all()
 
         res = getattr(dta, field)
         expected = getattr(dti._data, field)
diff --git a/pandas/tests/scalar/timestamp/test_timestamp.py b/pandas/tests/scalar/timestamp/test_timestamp.py
index 108d58bcc251d..89e5ce2241e42 100644
--- a/pandas/tests/scalar/timestamp/test_timestamp.py
+++ b/pandas/tests/scalar/timestamp/test_timestamp.py
@@ -802,10 +802,12 @@ def test_comparison(self, dt64, ts):
 
     def test_cmp_cross_reso(self):
         # numpy gets this wrong because of silent overflow
-        dt64 = np.datetime64(106752, "D")  # won't fit in M8[ns]
+        dt64 = np.datetime64(9223372800, "s")  # won't fit in M8[ns]
         ts = Timestamp._from_dt64(dt64)
 
-        other = Timestamp(dt64 - 1)
+        # subtracting 3600*24 gives a datetime64 that _can_ fit inside the
+        #  nanosecond implementation bounds.
+        other = Timestamp(dt64 - 3600 * 24)
         assert other < ts
         assert other.asm8 > ts.asm8  # <- numpy gets this wrong
         assert ts > other

From 9e3a7c2bb60301a8496f36ecdc748b6b6c65c8d3 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Thu, 9 Jun 2022 18:11:29 -0700
Subject: [PATCH 2/2] mypy fixup

---
 pandas/_libs/tslibs/timestamps.pyi | 4 ++++
 pandas/_libs/tslibs/vectorized.pyi | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/pandas/_libs/tslibs/timestamps.pyi b/pandas/_libs/tslibs/timestamps.pyi
index 4be9621a594dc..fd593ae453ef7 100644
--- a/pandas/_libs/tslibs/timestamps.pyi
+++ b/pandas/_libs/tslibs/timestamps.pyi
@@ -59,6 +59,10 @@ class Timestamp(datetime):
     # While Timestamp can return pd.NaT, having the constructor return
     # a Union with NaTType makes things awkward for users of pandas
     def _set_freq(self, freq: BaseOffset | None) -> None: ...
+    @classmethod
+    def _from_value_and_reso(
+        cls, value: int, reso: int, tz: _tzinfo | None
+    ) -> Timestamp: ...
     @property
     def year(self) -> int: ...
     @property
diff --git a/pandas/_libs/tslibs/vectorized.pyi b/pandas/_libs/tslibs/vectorized.pyi
index 919457724606d..8820a17ce5996 100644
--- a/pandas/_libs/tslibs/vectorized.pyi
+++ b/pandas/_libs/tslibs/vectorized.pyi
@@ -37,5 +37,7 @@ def ints_to_pydatetime(
     box: str = ...,
 ) -> npt.NDArray[np.object_]: ...
 def tz_convert_from_utc(
-    stamps: npt.NDArray[np.int64], tz: tzinfo | None
+    stamps: npt.NDArray[np.int64],
+    tz: tzinfo | None,
+    reso: int = ...,
 ) -> npt.NDArray[np.int64]: ...