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

doc/source/whatsnew/v1.2.0.rst

@@ -80,6 +80,7 @@ Datetimelike
 ^^^^^^^^^^^^
 - Bug in :attr:`DatetimeArray.date` where a ``ValueError`` would be raised with a read-only backing array (:issue:`33530`)
 - Bug in ``NaT`` comparisons failing to raise ``TypeError`` on invalid inequality comparisons (:issue:`35046`)
+- 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

@@ -989,13 +989,6 @@ 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/io/generate_legacy_storage_files.py

@@ -6,10 +6,10 @@
 in ~/pandas
 
 . activate pandas_0.20.3
-cd ~/
+cd ~/pandas/pandas
 
-$ python pandas/pandas/tests/io/generate_legacy_storage_files.py \
-    pandas/pandas/tests/io/data/legacy_pickle/0.20.3/ pickle
+$ python -m tests.io.generate_legacy_storage_files \
+    tests/io/data/legacy_pickle/0.20.3/ pickle
 
 This script generates a storage file for the current arch, system,
 and python version
@@ -328,7 +328,7 @@ def write_legacy_pickles(output_dir):
     pth = f"{platform_name()}.pickle"
 
     fh = open(os.path.join(output_dir, pth), "wb")
-    pickle.dump(create_pickle_data(), fh, pickle.HIGHEST_PROTOCOL)
+    pickle.dump(create_pickle_data(), fh, pickle.DEFAULT_PROTOCOL)
     fh.close()
 
     print(f"created pickle file: {pth}")

pandas/tests/tseries/offsets/test_offsets.py

@@ -635,22 +635,6 @@ 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):
-        offsets = {
-            "DateOffset": DateOffset(years=1),
-            "MonthBegin": MonthBegin(1),
-            "Day": Day(1),
-            "YearBegin": YearBegin(1),
-            "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:
-        # with open(pickle_path, 'wb') as f: pickle.dump(offsets, f)
-        #
-        result = read_pickle(pickle_path)
-        tm.assert_dict_equal(offsets, result)
-
     def test_pickle_roundtrip(self, offset_types):
         off = self._get_offset(offset_types)
         res = tm.round_trip_pickle(off)
@@ -664,6 +648,15 @@ 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)