[BUG] fixed DateOffset pickle bug when months >= 12

doc/source/whatsnew/v1.1.0.rst

@@ -900,6 +900,7 @@ Datetimelike
   resolution which converted to object dtype instead of coercing to ``datetime64[ns]``
   dtype when within the timestamp bounds (:issue:`34843`).
 - The ``freq`` keyword in :class:`Period`, :func:`date_range`, :func:`period_range`, :func:`pd.tseries.frequencies.to_offset` no longer allows tuples, pass as string instead (:issue:`34703`)
+- Bug in :class:`DateOffset` where attributes reconstructed from pickle files differ from original objects when input values exceed normal ranges (e.g months=12) (:issue:`34511`)
 
 Timedelta
 ^^^^^^^^^

pandas/_libs/tslibs/offsets.pyx

@@ -938,13 +938,6 @@ cdef class RelativeDeltaOffset(BaseOffset):
             state["_offset"] = state.pop("offset")
             state["kwds"]["offset"] = state["_offset"]
 
-        if "_offset" in state and not isinstance(state["_offset"], timedelta):
-            # relativedelta, we need to populate using its kwds
-            offset = state["_offset"]
-            odict = offset.__dict__
-            kwds = {key: odict[key] for key in odict if odict[key]}
-            state.update(kwds)
-
         self.n = state.pop("n")
         self.normalize = state.pop("normalize")
         self._cache = state.pop("_cache", {})

pandas/tests/tseries/offsets/test_offsets.py

@@ -635,7 +635,7 @@ def test_add_empty_datetimeindex(self, offset_types, tz_naive_fixture):
             result = offset_s + dta
         tm.assert_equal(result, dta)
 
-    def test_pickle_v0_15_2(self, datapath):
+    def test_pickle_v1_1_0(self, datapath):
         offsets = {
             "DateOffset": DateOffset(years=1),
             "MonthBegin": MonthBegin(1),
@@ -644,8 +644,8 @@ def test_pickle_v0_15_2(self, datapath):
             "Week": Week(1),
         }
 
-        pickle_path = datapath("tseries", "offsets", "data", "dateoffset_0_15_2.pickle")
-        # This code was executed once on v0.15.2 to generate the pickle:
+        pickle_path = datapath("tseries", "offsets", "data", "dateoffset_1_1_0.pickle")
+        # This code was executed once on v1.1.0 to generate the pickle:
         # with open(pickle_path, 'wb') as f: pickle.dump(offsets, f)
         #
         result = read_pickle(pickle_path)
@@ -664,6 +664,15 @@ def test_pickle_roundtrip(self, offset_types):
                 # Make sure nothings got lost from _params (which __eq__) is based on
                 assert getattr(off, attr) == getattr(res, attr)
 
+    def test_pickle_dateoffset_odd_inputs(self):
+        # GH#34511
+        off = DateOffset(months=12)
+        res = tm.round_trip_pickle(off)
+        assert off == res
+
+        base_dt = datetime(2020, 1, 1)
+        assert base_dt + off == base_dt + res
+
     def test_onOffset_deprecated(self, offset_types):
         # GH#30340 use idiomatic naming
         off = self._get_offset(offset_types)