ENH: Add empty property to Index.

Previously, attempting to evaluate an Index in a boolean context prints
an error message listing various alternatives, one of which is `.empty`,
which was not actually implemented on `Index`.

Author: Scott Sanderson

doc/source/whatsnew/v0.20.0.txt

@@ -146,6 +146,7 @@ Other enhancements
 - ``Series/DataFrame.asfreq()`` have gained a ``fill_value`` parameter, to fill missing values (:issue:`3715`).
 - ``Series/DataFrame.resample.asfreq`` have gained a ``fill_value`` parameter, to fill missing values during resampling (:issue:`3715`).
 - ``pandas.tools.hashing`` has gained a ``hash_tuples`` routine, and ``hash_pandas_object`` has gained the ability to hash a ``MultiIndex`` (:issue:`15224`)
+- Added ``.empty`` property to subclasses of ``Index``. (:issue:`15270`)
 
 .. _ISO 8601 duration: https://en.wikipedia.org/wiki/ISO_8601#Durations
 

pandas/core/base.py

@@ -877,6 +877,10 @@ def _values(self):
         """ the internal implementation """
         return self.values
 
+    @property
+    def empty(self):
+        return not self.values.size
+
     def max(self):
         """ The maximum value of the object """
         return nanops.nanmax(self.values)

pandas/tests/indexes/common.py

@@ -879,3 +879,9 @@ def test_fillna(self):
                 expected[1] = True
                 self.assert_numpy_array_equal(idx._isnan, expected)
                 self.assertTrue(idx.hasnans)
+
+    def test_empty(self):
+        # GH 15270
+        index = self.create_index()
+        self.assertFalse(index.empty)
+        self.assertTrue(index[:0].empty)