ENH: Allow Timestamp to accept Nanosecond argument (#19889)

doc/source/whatsnew/v0.23.0.txt

@@ -618,6 +618,7 @@ Datetimelike API Changes
 - Subtraction of :class:`Series` with timezone-aware ``dtype='datetime64[ns]'`` with mis-matched timezones will raise ``TypeError`` instead of ``ValueError`` (:issue:`18817`)
 - :func:`pandas.merge` provides a more informative error message when trying to merge on timezone-aware and timezone-naive columns (:issue:`15800`)
 - For :class:`DatetimeIndex` and :class:`TimedeltaIndex` with ``freq=None``, addition or subtraction of integer-dtyped array or ``Index`` will raise ``NullFrequencyError`` instead of ``TypeError`` (:issue:`19895`)
+- :class:`Timestamp` constructor now accepts a `nanosecond` keyword or positional argument (:issue:`18898`)
 
 .. _whatsnew_0230.api.other:
 

pandas/_libs/tslibs/conversion.pxd

@@ -16,7 +16,8 @@ cdef class _TSObject:
 
 
 cdef convert_to_tsobject(object ts, object tz, object unit,
-                         bint dayfirst, bint yearfirst)
+                         bint dayfirst, bint yearfirst,
+                         int32_t nanos=*)
 
 cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
                                             int32_t nanos=*)

pandas/_libs/tslibs/conversion.pyx

@@ -252,7 +252,7 @@ cpdef int64_t pydt_to_i8(object pydt) except? -1:
 
 
 cdef convert_to_tsobject(object ts, object tz, object unit,
-                         bint dayfirst, bint yearfirst):
+                         bint dayfirst, bint yearfirst, int32_t nanos=0):
     """
     Extract datetime and int64 from any of:
         - np.int64 (with unit providing a possible modifier)
@@ -297,7 +297,7 @@ cdef convert_to_tsobject(object ts, object tz, object unit,
             obj.value = ts
             dt64_to_dtstruct(ts, &obj.dts)
     elif PyDateTime_Check(ts):
-        return convert_datetime_to_tsobject(ts, tz)
+        return convert_datetime_to_tsobject(ts, tz, nanos)
     elif PyDate_Check(ts):
         # Keep the converter same as PyDateTime's
         ts = datetime.combine(ts, datetime_time())

pandas/_libs/tslibs/timestamps.pyx

@@ -107,6 +107,7 @@ cdef class _Timestamp(datetime):
     cdef readonly:
         int64_t value, nanosecond
         object freq       # frequency reference
+        list _date_attributes
 
     def __hash__(_Timestamp self):
         if self.nanosecond:
@@ -425,6 +426,8 @@ class Timestamp(_Timestamp):
         .. versionadded:: 0.19.0
     hour, minute, second, microsecond : int, optional, default 0
         .. versionadded:: 0.19.0
+    nanosecond : int, optional, default 0
+        .. versionadded:: 0.23.0
     tzinfo : datetime.tzinfo, optional, default None
         .. versionadded:: 0.19.0
 
@@ -556,7 +559,7 @@ class Timestamp(_Timestamp):
                 object freq=None, tz=None, unit=None,
                 year=None, month=None, day=None,
                 hour=None, minute=None, second=None, microsecond=None,
-                tzinfo=None):
+                nanosecond=None, tzinfo=None):
         # The parameter list folds together legacy parameter names (the first
         # four) and positional and keyword parameter names from pydatetime.
         #
@@ -580,6 +583,9 @@ class Timestamp(_Timestamp):
 
         cdef _TSObject ts
 
+        _date_attributes = [year, month, day, hour, minute, second,
+                            microsecond, nanosecond]
+
         if tzinfo is not None:
             if not PyTZInfo_Check(tzinfo):
                 # tzinfo must be a datetime.tzinfo object, GH#17690
@@ -588,28 +594,35 @@ class Timestamp(_Timestamp):
             elif tz is not None:
                 raise ValueError('Can provide at most one of tz, tzinfo')
 
-        if ts_input is _no_input:
+        if is_string_object(ts_input):
+            # User passed a date string to parse.
+            # Check that the user didn't also pass a date attribute kwarg.
+            if any(arg is not None for arg in _date_attributes):
+                raise ValueError('Cannot pass a date attribute keyword '
+                                 'argument when passing a date string')
+
+        elif ts_input is _no_input:
             # User passed keyword arguments.
             if tz is None:
                 # Handle the case where the user passes `tz` and not `tzinfo`
                 tz = tzinfo
             return Timestamp(datetime(year, month, day, hour or 0,
                                       minute or 0, second or 0,
                                       microsecond or 0, tzinfo),
-                             tz=tz)
+                             nanosecond=nanosecond, tz=tz)
         elif is_integer_object(freq):
             # User passed positional arguments:
             # Timestamp(year, month, day[, hour[, minute[, second[,
-            # microsecond[, tzinfo]]]]])
+            # microsecond[, nanosecond[, tzinfo]]]]]])
             return Timestamp(datetime(ts_input, freq, tz, unit or 0,
                                       year or 0, month or 0, day or 0,
-                                      hour), tz=hour)
+                                      minute), nanosecond=hour, tz=minute)
 
         if tzinfo is not None:
             # User passed tzinfo instead of tz; avoid silently ignoring
             tz, tzinfo = tzinfo, None
 
-        ts = convert_to_tsobject(ts_input, tz, unit, 0, 0)
+        ts = convert_to_tsobject(ts_input, tz, unit, 0, 0, nanosecond or 0)
 
         if ts.value == NPY_NAT:
             return NaT

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -385,6 +385,27 @@ def test_constructor_fromordinal(self):
         ts = Timestamp.fromordinal(dt_tz.toordinal(), tz='US/Eastern')
         assert ts.to_pydatetime() == dt_tz
 
+    @pytest.mark.parametrize('result', [
+        Timestamp(datetime(2000, 1, 2, 3, 4, 5, 6), nanosecond=1),
+        Timestamp(year=2000, month=1, day=2, hour=3, minute=4, second=5,
+                  microsecond=6, nanosecond=1),
+        Timestamp(year=2000, month=1, day=2, hour=3, minute=4, second=5,
+                  microsecond=6, nanosecond=1, tz='UTC'),
+        Timestamp(2000, 1, 2, 3, 4, 5, 6, 1, None),
+        Timestamp(2000, 1, 2, 3, 4, 5, 6, 1, pytz.UTC)])
+    def test_constructor_nanosecond(self, result):
+        # GH 18898
+        expected = Timestamp(datetime(2000, 1, 2, 3, 4, 5, 6), tz=result.tz)
+        expected = expected + Timedelta(nanoseconds=1)
+        assert result == expected
+
+    @pytest.mark.parametrize('arg', ['year', 'month', 'day', 'hour', 'minute',
+                                     'second', 'microsecond', 'nanosecond'])
+    def test_invalid_date_kwarg_with_string_input(self, arg):
+        kwarg = {arg: 1}
+        with pytest.raises(ValueError):
+            Timestamp('2010-10-10 12:59:59.999999999', **kwarg)
+
     def test_out_of_bounds_value(self):
         one_us = np.timedelta64(1).astype('timedelta64[us]')