BUG: DatetimeIndex with dayfirst/yearfirst and tz (pandas-dev#55813)

* BUG: DatetimeIndex with dayfirst/yearfirst and tz

* GH ref

doc/source/whatsnew/v2.2.0.rst

@@ -343,6 +343,7 @@ Categorical
 
 Datetimelike
 ^^^^^^^^^^^^
+- Bug in :class:`DatetimeIndex` construction when passing both a ``tz`` and either ``dayfirst`` or ``yearfirst`` ignoring dayfirst/yearfirst (:issue:`55813`)
 - Bug in :class:`DatetimeIndex` when passing an object-dtype ndarray of float objects and a ``tz`` incorrectly localizing the result (:issue:`55780`)
 - Bug in :func:`concat` raising ``AttributeError`` when concatenating all-NA DataFrame with :class:`DatetimeTZDtype` dtype DataFrame. (:issue:`52093`)
 - Bug in :func:`to_datetime` and :class:`DatetimeIndex` when passing a list of mixed-string-and-numeric types incorrectly raising (:issue:`55780`)

pandas/_libs/tslib.pyi

@@ -29,5 +29,9 @@ def array_to_datetime(
 # returned ndarray may be object dtype or datetime64[ns]
 
 def array_to_datetime_with_tz(
-    values: npt.NDArray[np.object_], tz: tzinfo, creso: int
+    values: npt.NDArray[np.object_],
+    tz: tzinfo,
+    dayfirst: bool,
+    yearfirst: bool,
+    creso: int,
 ) -> npt.NDArray[np.int64]: ...

pandas/_libs/tslib.pyx

@@ -61,6 +61,7 @@ from pandas._libs.tslibs.conversion cimport (
     _TSObject,
     cast_from_unit,
     convert_str_to_tsobject,
+    convert_to_tsobject,
     get_datetime64_nanos,
     parse_pydatetime,
 )
@@ -673,7 +674,9 @@ cdef _array_to_datetime_object(
     return oresult_nd, None
 
 
-def array_to_datetime_with_tz(ndarray values, tzinfo tz, NPY_DATETIMEUNIT creso):
+def array_to_datetime_with_tz(
+    ndarray values, tzinfo tz, bint dayfirst, bint yearfirst, NPY_DATETIMEUNIT creso
+):
     """
     Vectorized analogue to pd.Timestamp(value, tz=tz)
 
@@ -689,7 +692,7 @@ def array_to_datetime_with_tz(ndarray values, tzinfo tz, NPY_DATETIMEUNIT creso)
         Py_ssize_t i, n = values.size
         object item
         int64_t ival
-        datetime ts
+        _TSObject tsobj
 
     for i in range(n):
         # Analogous to `item = values[i]`
@@ -700,17 +703,12 @@ def array_to_datetime_with_tz(ndarray values, tzinfo tz, NPY_DATETIMEUNIT creso)
             ival = NPY_NAT
 
         else:
-            if PyDateTime_Check(item) and item.tzinfo is not None:
-                # We can't call Timestamp constructor with a tz arg, have to
-                #  do 2-step
-                ts = Timestamp(item).tz_convert(tz)
-            else:
-                ts = Timestamp(item, tz=tz)
-            if ts is NaT:
-                ival = NPY_NAT
-            else:
-                ts = (<_Timestamp>ts)._as_creso(creso)
-                ival = ts._value
+            tsobj = convert_to_tsobject(
+                item, tz=tz, unit="ns", dayfirst=dayfirst, yearfirst=yearfirst, nanos=0
+            )
+            if tsobj.value != NPY_NAT:
+                tsobj.ensure_reso(creso, item, round_ok=True)
+            ival = tsobj.value
 
         # Analogous to: result[i] = ival
         (<int64_t*>cnp.PyArray_MultiIter_DATA(mi, 0))[0] = ival

pandas/_libs/tslibs/conversion.pxd

@@ -24,7 +24,9 @@ cdef class _TSObject:
         bint fold
         NPY_DATETIMEUNIT creso
 
-    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso, str val=*) except? -1
+    cdef int64_t ensure_reso(
+        self, NPY_DATETIMEUNIT creso, val=*, bint round_ok=*
+    ) except? -1
 
 
 cdef _TSObject convert_to_tsobject(object ts, tzinfo tz, str unit,

pandas/_libs/tslibs/conversion.pyx

@@ -235,10 +235,14 @@ cdef class _TSObject:
         self.fold = 0
         self.creso = NPY_FR_ns  # default value
 
-    cdef int64_t ensure_reso(self, NPY_DATETIMEUNIT creso, str val=None) except? -1:
+    cdef int64_t ensure_reso(
+        self, NPY_DATETIMEUNIT creso, val=None, bint round_ok=False
+    ) except? -1:
         if self.creso != creso:
             try:
-                self.value = convert_reso(self.value, self.creso, creso, False)
+                self.value = convert_reso(
+                    self.value, self.creso, creso, round_ok=round_ok
+                )
             except OverflowError as err:
                 if val is not None:
                     raise OutOfBoundsDatetime(
@@ -283,6 +287,11 @@ cdef _TSObject convert_to_tsobject(object ts, tzinfo tz, str unit,
         obj.value = get_datetime64_nanos(ts, reso)
         if obj.value != NPY_NAT:
             pandas_datetime_to_datetimestruct(obj.value, reso, &obj.dts)
+            if tz is not None:
+                # GH#24559, GH#42288 We treat np.datetime64 objects as *wall* times
+                obj.value = tz_localize_to_utc_single(
+                    obj.value, tz, ambiguous="raise", nonexistent=None, creso=reso
+                )
     elif is_integer_object(ts):
         try:
             ts = <int64_t>ts

pandas/_libs/tslibs/timestamps.pyx

@@ -1873,10 +1873,6 @@ class Timestamp(_Timestamp):
                              "the tz parameter. Use tz_convert instead.")
 
         tzobj = maybe_get_tz(tz)
-        if tzobj is not None and is_datetime64_object(ts_input):
-            # GH#24559, GH#42288 As of 2.0 we treat datetime64 as
-            #  wall-time (consistent with DatetimeIndex)
-            return cls(ts_input).tz_localize(tzobj)
 
         if nanosecond is None:
             nanosecond = 0

pandas/core/arrays/datetimes.py

@@ -2240,10 +2240,13 @@ def _sequence_to_dt64(
         if lib.infer_dtype(data, skipna=False) == "integer":
             data = data.astype(np.int64)
         elif tz is not None and ambiguous == "raise":
-            # TODO: yearfirst/dayfirst/etc?
             obj_data = np.asarray(data, dtype=object)
             i8data = tslib.array_to_datetime_with_tz(
-                obj_data, tz, abbrev_to_npy_unit(out_unit)
+                obj_data,
+                tz=tz,
+                dayfirst=dayfirst,
+                yearfirst=yearfirst,
+                creso=abbrev_to_npy_unit(out_unit),
             )
             return i8data.view(out_dtype), tz, None
         else:

pandas/tests/indexes/datetimes/test_constructors.py

@@ -1247,6 +1247,21 @@ def test_datetimeindex_constructor_misc(self):
         assert len(idx1) == len(idx2)
         assert idx1.freq == idx2.freq
 
+    def test_dti_constructor_object_dtype_dayfirst_yearfirst_with_tz(self):
+        # GH#55813
+        val = "5/10/16"
+
+        dfirst = Timestamp(2016, 10, 5, tz="US/Pacific")
+        yfirst = Timestamp(2005, 10, 16, tz="US/Pacific")
+
+        result1 = DatetimeIndex([val], tz="US/Pacific", dayfirst=True)
+        expected1 = DatetimeIndex([dfirst])
+        tm.assert_index_equal(result1, expected1)
+
+        result2 = DatetimeIndex([val], tz="US/Pacific", yearfirst=True)
+        expected2 = DatetimeIndex([yfirst])
+        tm.assert_index_equal(result2, expected2)
+
     def test_pass_datetimeindex_to_index(self):
         # Bugs in #1396
         rng = date_range("1/1/2000", "3/1/2000")