ENH: non-nano Timestamp.timestamp, to_period (#46990)

* ENH: Timestamp.timestamp non-nano

* ENH: Timestamp.to_period non-nano

* normalize prelims

Author: jbrockmendel

pandas/_libs/tslibs/dtypes.pxd

@@ -6,6 +6,7 @@ from pandas._libs.tslibs.np_datetime cimport NPY_DATETIMEUNIT
 cdef str npy_unit_to_abbrev(NPY_DATETIMEUNIT unit)
 cdef NPY_DATETIMEUNIT freq_group_code_to_npy_unit(int freq) nogil
 cdef int64_t periods_per_day(NPY_DATETIMEUNIT reso=*) except? -1
+cdef int64_t periods_per_second(NPY_DATETIMEUNIT reso) except? -1
 
 cdef dict attrname_to_abbrevs
 

pandas/_libs/tslibs/dtypes.pyx

@@ -348,6 +348,19 @@ cdef int64_t periods_per_day(NPY_DATETIMEUNIT reso=NPY_DATETIMEUNIT.NPY_FR_ns) e
     return day_units
 
 
+cdef int64_t periods_per_second(NPY_DATETIMEUNIT reso) except? -1:
+    if reso == NPY_DATETIMEUNIT.NPY_FR_ns:
+        return 1_000_000_000
+    elif reso == NPY_DATETIMEUNIT.NPY_FR_us:
+        return 1_000_000
+    elif reso == NPY_DATETIMEUNIT.NPY_FR_ms:
+        return 1_000
+    elif reso == NPY_DATETIMEUNIT.NPY_FR_s:
+        return 1
+    else:
+        raise NotImplementedError(reso)
+
+
 cdef dict _reso_str_map = {
     Resolution.RESO_NS.value: "nanosecond",
     Resolution.RESO_US.value: "microsecond",

pandas/_libs/tslibs/timestamps.pyx

@@ -52,7 +52,11 @@ from pandas._libs.tslibs.conversion cimport (
     convert_datetime_to_tsobject,
     convert_to_tsobject,
 )
-from pandas._libs.tslibs.dtypes cimport npy_unit_to_abbrev
+from pandas._libs.tslibs.dtypes cimport (
+    npy_unit_to_abbrev,
+    periods_per_day,
+    periods_per_second,
+)
 from pandas._libs.tslibs.util cimport (
     is_array,
     is_datetime64_object,
@@ -811,11 +815,12 @@ cdef class _Timestamp(ABCTimestamp):
         cdef:
             local_val = self._maybe_convert_value_to_local()
             int64_t normalized
+            int64_t ppd = periods_per_day(self._reso)
 
         if self._reso != NPY_FR_ns:
             raise NotImplementedError(self._reso)
 
-        normalized = normalize_i8_stamp(local_val)
+        normalized = normalize_i8_stamp(local_val, ppd)
         return Timestamp(normalized).tz_localize(self.tzinfo)
 
     # -----------------------------------------------------------------
@@ -834,8 +839,8 @@ cdef class _Timestamp(ABCTimestamp):
 
         if len(state) == 3:
             # pre-non-nano pickle
+            # TODO: no tests get here 2022-05-10
             reso = NPY_FR_ns
-            assert False  # checking for coverage
         else:
             reso = state[4]
         self._reso = reso
@@ -982,10 +987,10 @@ cdef class _Timestamp(ABCTimestamp):
         """
         # GH 17329
         # Note: Naive timestamps will not match datetime.stdlib
-        if self._reso != NPY_FR_ns:
-            raise NotImplementedError(self._reso)
 
-        return round(self.value / 1e9, 6)
+        denom = periods_per_second(self._reso)
+
+        return round(self.value / denom, 6)
 
     cpdef datetime to_pydatetime(_Timestamp self, bint warn=True):
         """
@@ -1080,9 +1085,6 @@ cdef class _Timestamp(ABCTimestamp):
         """
         from pandas import Period
 
-        if self._reso != NPY_FR_ns:
-            raise NotImplementedError(self._reso)
-
         if self.tz is not None:
             # GH#21333
             warnings.warn(
@@ -2252,16 +2254,18 @@ Timestamp.resolution = Timedelta(nanoseconds=1)  # GH#21336, GH#21365
 
 
 @cython.cdivision(False)
-cdef inline int64_t normalize_i8_stamp(int64_t local_val) nogil:
+cdef inline int64_t normalize_i8_stamp(int64_t local_val, int64_t ppd) nogil:
     """
     Round the localized nanosecond timestamp down to the previous midnight.
 
     Parameters
     ----------
     local_val : int64_t
+    ppd : int64_t
+        Periods per day in the Timestamp's resolution.
 
     Returns
     -------
     int64_t
     """
-    return local_val - (local_val % ccalendar.DAY_NANOS)
+    return local_val - (local_val % ppd)

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -840,3 +840,11 @@ def test_to_datetime64(self, dt64, ts):
         res = ts.to_datetime64()
         assert res == dt64
         assert res.dtype == dt64.dtype
+
+    def test_timestamp(self, dt64, ts):
+        alt = Timestamp(dt64)
+        assert ts.timestamp() == alt.timestamp()
+
+    def test_to_period(self, dt64, ts):
+        alt = Timestamp(dt64)
+        assert ts.to_period("D") == alt.to_period("D")