Component returns True if checked with bool()

https://github.com/collective/icalendar/issues/141

src/icalendar/cal.py

@@ -93,6 +93,21 @@ class Component(CaselessDict):
     #    """
     #    return name in not_compliant
 
+    def __bool__(self):
+        """
+        Returns True, CaselessDict would return False if it had no items
+        """
+        return True
+
+    # python 2 compatibility
+    __nonzero__ = __bool__
+
+    def is_empty(self):
+        """
+        Returns True if Component has no items or subcomponents, else False
+        """
+        return True if not (list(self.values()) + self.subcomponents) else False
+
     #############################
     # handling of property values
 

src/icalendar/tests/test_unit_cal.py

@@ -18,9 +18,14 @@ class TestCalComponent(unittest.TestCase):
         c = Component()
         c.name = 'VCALENDAR'
 
+        self.assertTrue(c)
+        self.assertTrue(c.is_empty())
+
         # Every key defines a property.A property can consist of either a
         # single item. This can be set with a single value...
         c['prodid'] = '-//max m//icalendar.mxm.dk/'
+        self.assertFalse(c.is_empty())
+
         self.assertEqual(
             c,
             Calendar({'PRODID': '-//max m//icalendar.mxm.dk/'})