BUG: Properly read Categorical msgpacks

Patches bug in read_msgpack in which
Series categoricals were accidentally
being constructed with a non-categorical
dtype, resulting in an error.

Closes gh-14901.

Author: gfyoung

doc/source/whatsnew/v0.20.0.txt

@@ -245,6 +245,7 @@ Bug Fixes
 
 
 
+- Bug in ``pd.read_msgpack()`` in which ``Series`` categoricals were being improperly processed (:issue:`14901`)
 
 
 

pandas/io/packers.py

@@ -595,11 +595,14 @@ def decode(obj):
         pd_dtype = pandas_dtype(dtype)
         np_dtype = pandas_dtype(dtype).base
 
+        # see gh-14901
+        klass_dtype = np_dtype if pd_dtype.name != 'category' else pd_dtype
+
         index = obj[u'index']
         result = globals()[obj[u'klass']](unconvert(obj[u'data'], dtype,
                                                     obj[u'compress']),
                                           index=index,
-                                          dtype=np_dtype,
+                                          dtype=klass_dtype,
                                           name=obj[u'name'])
         tz = getattr(pd_dtype, 'tz', None)
         if tz:

pandas/io/tests/test_packers.py

@@ -363,13 +363,17 @@ def setUp(self):
             'F': [Timestamp('20130102', tz='US/Eastern')] * 2 +
                  [Timestamp('20130603', tz='CET')] * 3,
             'G': [Timestamp('20130102', tz='US/Eastern')] * 5,
+            'H': Categorical([1, 2, 3, 4, 5]),
+            'I': Categorical([1, 2, 3, 4, 5], ordered=True),
         }
 
         self.d['float'] = Series(data['A'])
         self.d['int'] = Series(data['B'])
         self.d['mixed'] = Series(data['E'])
         self.d['dt_tz_mixed'] = Series(data['F'])
         self.d['dt_tz'] = Series(data['G'])
+        self.d['cat_ordered'] = Series(data['H'])
+        self.d['cat_unordered'] = Series(data['I'])
 
     def test_basic(self):