Fixed special case for astype

Author: TomAugspurger

pandas/core/internals.py

@@ -141,6 +141,7 @@ def is_categorical_astype(self, dtype):
             if dtype == CategoricalDtype():
                 return True
 
+        elif dtype is Categorical:
             # this is a pd.Categorical, but is not
             # a valid type for astypeing
             raise TypeError("invalid type {0} for astype".format(dtype))

pandas/tests/test_categorical.py

@@ -4149,12 +4149,6 @@ def f():
         df = pd.DataFrame({'a': pd.Categorical(idx)})
         tm.assert_frame_equal(df.fillna(value=pd.NaT), df)
 
-    def test_astype_new(self):
-        s = self.cat['value_group']
-        r1 = s.astype('object')
-        r2 = r1.astype('category')
-        tm.assert_series_equal(r2, s)
-
     def test_astype_to_other(self):
 
         s = self.cat['value_group']
@@ -4197,9 +4191,9 @@ def cmp(a, b):
             tm.assert_series_equal(result, s, check_categorical=False)
 
         # invalid conversion (these are NOT a dtype)
-        # for invalid in [lambda x: x.astype(pd.Categorical),
-        #                 lambda x: x.astype('object').astype(pd.Categorical)]:
-        #     pytest.raises(TypeError, lambda: invalid(s))
+        for invalid in [lambda x: x.astype(pd.Categorical),
+                        lambda x: x.astype('object').astype(pd.Categorical)]:
+            pytest.raises(TypeError, lambda: invalid(s))
 
     def test_astype_categorical(self):