FIX: add nbytes property in Categorical

Author: jankatins

pandas/core/categorical.py

@@ -722,6 +722,10 @@ def __array__(self, dtype=None):
     def T(self):
         return self
 
+    @property
+    def nbytes(self):
+        return self._codes.nbytes + self._categories.values.nbytes
+
     def isnull(self):
         """
         Detect missing values

pandas/tests/test_categorical.py

@@ -884,6 +884,11 @@ def test_set_item_nan(self):
         exp = np.array([0,1,3,2])
         self.assert_numpy_array_equal(cat.codes, exp)
 
+    def test_nbytes(self):
+        cat = pd.Categorical([1,2,3])
+        exp = cat._codes.nbytes + cat._categories.values.nbytes
+        self.assertEqual(cat.nbytes, exp)
+
     def test_deprecated_labels(self):
         # TODO: labels is deprecated and should be removed in 0.18 or 2017, whatever is earlier
         cat = pd.Categorical([1,2,3, np.nan], categories=[1,2,3])