REF: avoid parse_datetime_string in tslib

pandas/_libs/tslib.pyx

@@ -35,7 +35,6 @@ from pandas._libs.tslibs.np_datetime cimport (
     npy_datetimestruct_to_datetime,
     pandas_datetime_to_datetimestruct,
     pydate_to_dt64,
-    pydatetime_to_dt64,
     string_to_dts,
 )
 from pandas._libs.tslibs.strptime cimport parse_today_now
@@ -46,7 +45,6 @@ from pandas._libs.util cimport (
 )
 
 from pandas._libs.tslibs.np_datetime import OutOfBoundsDatetime
-from pandas._libs.tslibs.parsing import parse_datetime_string
 
 from pandas._libs.tslibs.conversion cimport (
     _TSObject,
@@ -542,13 +540,7 @@ cpdef array_to_datetime(
                 _ts = convert_str_to_tsobject(
                     val, None, unit="ns", dayfirst=dayfirst, yearfirst=yearfirst
                 )
-                try:
-                    _ts.ensure_reso(NPY_FR_ns)
-                except OutOfBoundsDatetime as err:
-                    # re-raise with better exception message
-                    raise OutOfBoundsDatetime(
-                        f"Out of bounds nanosecond timestamp: {val}"
-                    ) from err
+                _ts.ensure_reso(NPY_FR_ns, val)
 
                 iresult[i] = _ts.value
 
@@ -698,6 +690,7 @@ cdef _array_to_datetime_object(
         ndarray[object] oresult
         npy_datetimestruct dts
         cnp.broadcast mi
+        _TSObject tsobj
 
     assert is_raise or is_ignore or is_coerce
 
@@ -725,20 +718,20 @@ cdef _array_to_datetime_object(
                 oresult[i] = "NaT"
                 cnp.PyArray_MultiIter_NEXT(mi)
                 continue
-            elif val == "now":
-                oresult[i] = datetime.now()
-                cnp.PyArray_MultiIter_NEXT(mi)
-                continue
-            elif val == "today":
-                oresult[i] = datetime.today()
-                cnp.PyArray_MultiIter_NEXT(mi)
-                continue
 
             try:
-                oresult[i] = parse_datetime_string(val, dayfirst=dayfirst,
-                                                   yearfirst=yearfirst)
-                pydatetime_to_dt64(oresult[i], &dts)
-                check_dts_bounds(&dts)
+                tsobj = convert_str_to_tsobject(
+                    val, None, unit="ns", dayfirst=dayfirst, yearfirst=yearfirst
+                )
+                tsobj.ensure_reso(NPY_FR_ns, val)
+
+                dts = tsobj.dts
+                oresult[i] = datetime(
+                    dts.year, dts.month, dts.day, dts.hour, dts.min, dts.sec, dts.us,
+                    tzinfo=tsobj.tzinfo,
+                    fold=tsobj.fold,
+                )
+
             except (ValueError, OverflowError) as ex:
                 ex.args = (f"{ex}, at position {i}", )
                 if is_coerce:

pandas/_libs/tslibs/conversion.pxd

@@ -24,7 +24,7 @@ cdef class _TSObject:
         bint fold
         NPY_DATETIMEUNIT creso
 
-    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso) except? -1
+    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso, str val=*) except? -1
 
 
 cdef _TSObject convert_to_tsobject(object ts, tzinfo tz, str unit,

pandas/_libs/tslibs/conversion.pyx

@@ -212,11 +212,15 @@ cdef class _TSObject:
         self.fold = 0
         self.creso = NPY_FR_ns  # default value
 
-    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso) except? -1:
+    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso, str val=None) except? -1:
         if self.creso != creso:
             try:
                 self.value = convert_reso(self.value, self.creso, creso, False)
             except OverflowError as err:
+                if val is not None:
+                    raise OutOfBoundsDatetime(
+                        f"Out of bounds nanosecond timestamp: {val}"
+                    ) from err
                 raise OutOfBoundsDatetime from err
 
             self.creso = creso