BUG: Fixed msgpack roundtrip with PeriodIndex (#24335)

Closes #24135

Author: TomAugspurger

pandas/core/indexes/period.py

@@ -227,6 +227,8 @@ def _simple_new(cls, values, name=None, freq=None, **kwargs):
             values = np.asarray(values)
         if is_float_dtype(values):
             raise TypeError("PeriodIndex._simple_new does not accept floats.")
+        if freq:
+            freq = Period._maybe_convert_freq(freq)
         values = PeriodArray(values, freq=freq)
 
         if not isinstance(values, PeriodArray):

pandas/io/packers.py

@@ -605,7 +605,7 @@ def decode(obj):
     elif typ == u'datetime_index':
         data = unconvert(obj[u'data'], np.int64, obj.get(u'compress'))
         d = dict(name=obj[u'name'], freq=obj[u'freq'])
-        result = DatetimeIndex._simple_new(data, **d)
+        result = DatetimeIndex(data, **d)
         tz = obj[u'tz']
 
         # reverse tz conversion

pandas/tests/io/test_packers.py

@@ -940,3 +940,9 @@ def test_msgpacks_legacy(self, current_packers_data, all_packers_data,
         except ImportError:
             # blosc not installed
             pass
+
+    def test_msgpack_period_freq(self):
+        # https://github.com/pandas-dev/pandas/issues/24135
+        s = Series(np.random.rand(5), index=date_range('20130101', periods=5))
+        r = read_msgpack(s.to_msgpack())
+        repr(r)