ENH: Timestamp.month_name, day_name support non-nano (pandas-dev#46959)

* ENH: Timestamp.month_name, day_name support non-nano

* restore comment

Author: jbrockmendel

asv_bench/benchmarks/tslibs/fields.py

@@ -66,9 +66,9 @@ class TimeGetStartEndField:
 
     def setup(self, size, side, period, freqstr, month_kw):
         arr = np.random.randint(0, 10, size=size, dtype="i8")
-        self.dt64data = arr.view("M8[ns]")
+        self.i8data = arr
 
         self.attrname = f"is_{period}_{side}"
 
     def time_get_start_end_field(self, size, side, period, freqstr, month_kw):
-        get_start_end_field(self.dt64data, self.attrname, freqstr, month_kw=month_kw)
+        get_start_end_field(self.i8data, self.attrname, freqstr, month_kw=month_kw)

pandas/_libs/tslibs/fields.pyi

@@ -10,12 +10,14 @@ def get_date_name_field(
     dtindex: npt.NDArray[np.int64],  # const int64_t[:]
     field: str,
     locale: str | None = ...,
+    reso: int = ...,  # NPY_DATETIMEUNIT
 ) -> npt.NDArray[np.object_]: ...
 def get_start_end_field(
-    dt64values: npt.NDArray[np.datetime64],
+    dtindex: npt.NDArray[np.int64],
     field: str,
     freqstr: str | None = ...,
     month_kw: int = ...,
+    reso: int = ...,  # NPY_DATETIMEUNIT
 ) -> npt.NDArray[np.bool_]: ...
 def get_date_field(
     dtindex: npt.NDArray[np.int64],  # const int64_t[:]

pandas/_libs/tslibs/fields.pyx

@@ -44,6 +44,7 @@ from pandas._libs.tslibs.ccalendar cimport (
 from pandas._libs.tslibs.nattype cimport NPY_NAT
 from pandas._libs.tslibs.np_datetime cimport (
     NPY_DATETIMEUNIT,
+    NPY_FR_ns,
     dt64_to_dtstruct,
     get_unit_from_dtype,
     npy_datetimestruct,
@@ -139,13 +140,18 @@ def month_position_check(fields, weekdays) -> str | None:
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_date_name_field(const int64_t[:] dtindex, str field, object locale=None):
+def get_date_name_field(
+    const int64_t[:] dtindex,
+    str field,
+    object locale=None,
+    NPY_DATETIMEUNIT reso=NPY_FR_ns,
+):
     """
     Given a int64-based datetime index, return array of strings of date
     name based on requested field (e.g. day_name)
     """
     cdef:
-        Py_ssize_t i, count = len(dtindex)
+        Py_ssize_t i, count = dtindex.shape[0]
         ndarray[object] out, names
         npy_datetimestruct dts
         int dow
@@ -163,7 +169,7 @@ def get_date_name_field(const int64_t[:] dtindex, str field, object locale=None)
                 out[i] = np.nan
                 continue
 
-            dt64_to_dtstruct(dtindex[i], &dts)
+            pandas_datetime_to_datetimestruct(dtindex[i], reso, &dts)
             dow = dayofweek(dts.year, dts.month, dts.day)
             out[i] = names[dow].capitalize()
 
@@ -178,7 +184,7 @@ def get_date_name_field(const int64_t[:] dtindex, str field, object locale=None)
                 out[i] = np.nan
                 continue
 
-            dt64_to_dtstruct(dtindex[i], &dts)
+            pandas_datetime_to_datetimestruct(dtindex[i], reso, &dts)
             out[i] = names[dts.month].capitalize()
 
     else:
@@ -201,35 +207,39 @@ cdef inline bint _is_on_month(int month, int compare_month, int modby) nogil:
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_start_end_field(ndarray dt64values, str field,
-                        str freqstr=None, int month_kw=12):
+def get_start_end_field(
+    const int64_t[:] dtindex,
+    str field,
+    str freqstr=None,
+    int month_kw=12,
+    NPY_DATETIMEUNIT reso=NPY_FR_ns,
+):
     """
     Given an int64-based datetime index return array of indicators
     of whether timestamps are at the start/end of the month/quarter/year
     (defined by frequency).
 
     Parameters
     ----------
-    dt64values : ndarray[datetime64], any resolution
+    dtindex : ndarray[int64]
     field : str
     frestr : str or None, default None
     month_kw : int, default 12
+    reso : NPY_DATETIMEUNIT, default NPY_FR_ns
 
     Returns
     -------
     ndarray[bool]
     """
     cdef:
         Py_ssize_t i
-        int count = dt64values.size
+        int count = dtindex.shape[0]
         bint is_business = 0
         int end_month = 12
         int start_month = 1
         ndarray[int8_t] out
         npy_datetimestruct dts
         int compare_month, modby
-        ndarray dtindex = dt64values.view("i8")
-        NPY_DATETIMEUNIT reso = get_unit_from_dtype(dt64values.dtype)
 
     out = np.zeros(count, dtype='int8')
 

pandas/_libs/tslibs/timestamps.pyx

@@ -487,7 +487,6 @@ cdef class _Timestamp(ABCTimestamp):
             dict kwds
             ndarray[uint8_t, cast=True] out
             int month_kw
-            str unit
 
         if freq:
             kwds = freq.kwds
@@ -499,9 +498,8 @@ cdef class _Timestamp(ABCTimestamp):
 
         val = self._maybe_convert_value_to_local()
 
-        unit = npy_unit_to_abbrev(self._reso)
-        out = get_start_end_field(np.array([val], dtype=f"M8[{unit}]"),
-                                  field, freqstr, month_kw)
+        out = get_start_end_field(np.array([val], dtype=np.int64),
+                                  field, freqstr, month_kw, self._reso)
         return out[0]
 
     cdef _warn_on_field_deprecation(self, freq, str field):
@@ -661,12 +659,10 @@ cdef class _Timestamp(ABCTimestamp):
             int64_t val
             object[::1] out
 
-        if self._reso != NPY_FR_ns:
-            raise NotImplementedError(self._reso)
-
         val = self._maybe_convert_value_to_local()
+
         out = get_date_name_field(np.array([val], dtype=np.int64),
-                                  field, locale=locale)
+                                  field, locale=locale, reso=self._reso)
         return out[0]
 
     def day_name(self, locale=None) -> str:

pandas/core/arrays/datetimes.py

@@ -38,11 +38,13 @@
     tz_convert_from_utc,
     tzconversion,
 )
+from pandas._libs.tslibs.np_datetime import py_get_unit_from_dtype
 from pandas._typing import npt
 from pandas.errors import (
     OutOfBoundsDatetime,
     PerformanceWarning,
 )
+from pandas.util._decorators import cache_readonly
 from pandas.util._exceptions import find_stack_level
 from pandas.util._validators import validate_inclusive
 
@@ -131,7 +133,7 @@ def f(self):
                     month_kw = kwds.get("startingMonth", kwds.get("month", 12))
 
                 result = fields.get_start_end_field(
-                    values.view(self._ndarray.dtype), field, self.freqstr, month_kw
+                    values, field, self.freqstr, month_kw, reso=self._reso
                 )
             else:
                 result = fields.get_date_field(values, field)
@@ -140,7 +142,7 @@ def f(self):
             return result
 
         if field in self._object_ops:
-            result = fields.get_date_name_field(values, field)
+            result = fields.get_date_name_field(values, field, reso=self._reso)
             result = self._maybe_mask_results(result, fill_value=None)
 
         else:
@@ -544,6 +546,10 @@ def _check_compatible_with(self, other, setitem: bool = False):
     # -----------------------------------------------------------------
     # Descriptive Properties
 
+    @cache_readonly
+    def _reso(self):
+        return py_get_unit_from_dtype(self._ndarray.dtype)
+
     def _box_func(self, x: np.datetime64) -> Timestamp | NaTType:
         # GH#42228
         value = x.view("i8")
@@ -1270,7 +1276,9 @@ def month_name(self, locale=None):
         """
         values = self._local_timestamps()
 
-        result = fields.get_date_name_field(values, "month_name", locale=locale)
+        result = fields.get_date_name_field(
+            values, "month_name", locale=locale, reso=self._reso
+        )
         result = self._maybe_mask_results(result, fill_value=None)
         return result
 
@@ -1313,7 +1321,9 @@ def day_name(self, locale=None):
         """
         values = self._local_timestamps()
 
-        result = fields.get_date_name_field(values, "day_name", locale=locale)
+        result = fields.get_date_name_field(
+            values, "day_name", locale=locale, reso=self._reso
+        )
         result = self._maybe_mask_results(result, fill_value=None)
         return result
 

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -753,6 +753,14 @@ def test_start_end_fields(self, ts):
             assert not ts.is_month_end
             assert not ts.is_month_end
 
+    def test_day_name(self, dt64, ts):
+        alt = Timestamp(dt64)
+        assert ts.day_name() == alt.day_name()
+
+    def test_month_name(self, dt64, ts):
+        alt = Timestamp(dt64)
+        assert ts.month_name() == alt.month_name()
+
     def test_repr(self, dt64, ts):
         alt = Timestamp(dt64)
 

pandas/tests/tslibs/test_fields.py

@@ -28,10 +28,7 @@ def test_get_date_field_readonly(dtindex):
 
 
 def test_get_start_end_field_readonly(dtindex):
-    dt64values = dtindex.view("M8[ns]")
-    dt64values.flags.writeable = False
-
-    result = fields.get_start_end_field(dt64values, "is_month_start", None)
+    result = fields.get_start_end_field(dtindex, "is_month_start", None)
     expected = np.array([True, False, False, False, False], dtype=np.bool_)
     tm.assert_numpy_array_equal(result, expected)