ENH/API: implement __nonzero__ for NDFrame

RELEASE.rst

@@ -112,6 +112,7 @@ pandas 0.11.1
     - added top-level ``pd.read_sql`` and ``to_sql`` DataFrame methods
   - the ``method`` and ``axis`` arguments of ``DataFrame.replace()`` are
     deprecated
+  - Implement ``__nonzero__`` for ``NDFrame`` objects (GH3691_, GH3696_)
 
 **Bug Fixes**
 
@@ -266,6 +267,8 @@ pandas 0.11.1
 .. _GH3675: https://github.com/pydata/pandas/issues/3675
 .. _GH3682: https://github.com/pydata/pandas/issues/3682
 .. _GH3702: https://github.com/pydata/pandas/issues/3702
+.. _GH3691: https://github.com/pydata/pandas/issues/3691
+.. _GH3696: https://github.com/pydata/pandas/issues/3696
 
 pandas 0.11.0
 =============

doc/source/v0.11.1.txt

@@ -88,6 +88,8 @@ API changes
 
   - Add the keyword ``allow_duplicates`` to ``DataFrame.insert`` to allow a duplicate column
     to be inserted if ``True``, default is ``False`` (same as prior to 0.11.1) (GH3679_)
+  - Implement ``__nonzero__`` for ``NDFrame`` objects (GH3691_, GH3696_)
+
 
   - IO api
 

pandas/core/frame.py

@@ -595,14 +595,6 @@ def shape(self):
 
     #----------------------------------------------------------------------
     # Class behavior
-
-    @property
-    def empty(self):
-        return not (len(self.columns) > 0 and len(self.index) > 0)
-
-    def __nonzero__(self):
-        raise ValueError("Cannot call bool() on DataFrame.")
-
     def _repr_fits_vertical_(self):
         """
         Check length against max_rows.

pandas/core/generic.py

@@ -560,6 +560,13 @@ def values(self):
         return self._data.as_matrix()
 
     @property
+    def empty(self):
+        return not all(len(ax) > 0 for ax in self.axes)
+
+    def __nonzero__(self):
+        return not self.empty
+
+    @property
     def ndim(self):
         return self._data.ndim
 

pandas/tests/test_frame.py

@@ -10379,9 +10379,15 @@ def test_index_namedtuple(self):
         df = DataFrame([(1, 2), (3, 4)], index=index, columns=["A", "B"])
         self.assertEqual(df.ix[IndexType("foo", "bar")]["A"], 1)
 
-    def test_bool_raises_value_error_1069(self):
+    def test_bool_empty_nonzero(self):
         df = DataFrame([1, 2, 3])
-        self.failUnlessRaises(ValueError, lambda: bool(df))
+        self.assertTrue(bool(df))
+        self.assertFalse(df.empty)
+        df = DataFrame(index=['a', 'b'], columns=['c', 'd']).dropna()
+        self.assertFalse(bool(df))
+        self.assertFalse(bool(df.T))
+        self.assertTrue(df.empty)
+        self.assertTrue(df.T.empty)
 
     def test_any_all(self):
         self._check_bool_op('any', np.any, has_skipna=True, has_bool_only=True)