BUG: Fix inconsistency with DateOffset near DST

doc/source/whatsnew/v3.0.0.rst

@@ -721,6 +721,7 @@ Timedelta
 ^^^^^^^^^
 - Accuracy improvement in :meth:`Timedelta.to_pytimedelta` to round microseconds consistently for large nanosecond based Timedelta (:issue:`57841`)
 - Bug in :class:`Timedelta` constructor failing to raise when passed an invalid keyword (:issue:`53801`)
+- Bug in :class:`pandas.tseries.offsets.DateOffset` where ``DateOffset(1)`` and ``DateOffset(days=1)`` returned different results near daylight saving time transitions. (:issue:`61862`)
 - Bug in :meth:`DataFrame.cumsum` which was raising ``IndexError`` if dtype is ``timedelta64[ns]`` (:issue:`57956`)
 
 Timezones

pandas/_libs/tslibs/offsets.pyx

@@ -18,6 +18,8 @@ from cpython.datetime cimport (
 
 import warnings
 
+from dateutil.relativedelta import relativedelta
+
 import_datetime()
 
 import numpy as np
@@ -283,8 +285,9 @@ _relativedelta_kwds = {"years", "months", "weeks", "days", "year", "month",
 
 cdef _determine_offset(kwds):
     if not kwds:
-        # GH 45643/45890: (historically) defaults to 1 day
-        return timedelta(days=1), False
+        # GH 45643, 45890: (historically) defaults to 1 day
+        # GH 61870: changed from timedelta to relativedelta
+        return relativedelta(days=1), True
 
     if "millisecond" in kwds:
         raise NotImplementedError(
@@ -325,8 +328,6 @@ cdef _determine_offset(kwds):
         kwds_no_nanos["microseconds"] = kwds_no_nanos.get("microseconds", 0) + micro
 
     if all(k in kwds_use_relativedelta for k in kwds_no_nanos):
-        from dateutil.relativedelta import relativedelta
-
         return relativedelta(**kwds_no_nanos), True
 
     raise ValueError(

pandas/tests/tseries/offsets/test_offsets.py

@@ -9,6 +9,7 @@
     timedelta,
 )
 
+from dateutil.relativedelta import relativedelta
 import numpy as np
 import pytest
 
@@ -1095,9 +1096,9 @@ def test_dateoffset_misc():
 
 @pytest.mark.parametrize("n", [-1, 1, 3])
 def test_construct_int_arg_no_kwargs_assumed_days(n):
-    # GH 45890, 45643
+    # GH 45643, 45890, 61870
     offset = DateOffset(n)
-    assert offset._offset == timedelta(1)
+    assert offset._offset == relativedelta(days=1)
     result = Timestamp(2022, 1, 2) + offset
     expected = Timestamp(2022, 1, 2 + n)
     assert result == expected
@@ -1227,3 +1228,12 @@ def test_is_yqm_start_end():
 def test_multiply_dateoffset_typeerror(left, right):
     with pytest.raises(TypeError, match="Cannot multiply"):
         left * right
+
+
+def test_dateoffset_days_vs_n_near_dst_transition():
+    # GH 61870
+    ts = Timestamp("2022-10-30", tz="Europe/Brussels")
+
+    offset_days = ts + offsets.DateOffset(days=1)
+    offset_n = ts + offsets.DateOffset(1)
+    assert offset_days == offset_n