Allow searching descendants.

atom.py

@@ -233,6 +233,24 @@ def get_all_descendants(self):
 
         return descendants
 
+    def get_children_of_type(self, type):
+        children = []
+        if self.is_container():
+            [children.append(child) for child in self if child.type == type]
+
+        return children
+
+    def get_descendants_of_type(self, type):
+        descendants = []
+        if self.is_container():
+            for child in self:
+                if child.type == type:
+                    descendants.append(child)
+                descendants += child.get_descendants_of_type(type)
+
+        return descendants
+
+
     # File-like behaviours
 
     def next(self):

atomtest.py

@@ -386,6 +386,23 @@ def testGetAllDescendants(self):
         self.assertEqual(loaded_atom[0][1], descendants[2])
         self.assertEqual(loaded_atom[1], descendants[3])
 
+    def testGetChildrenOfType(self):
+        loaded_atom = atom.Atom(self.atom_stream)
+        children_of_type = loaded_atom.get_children_of_type(self.child_1_type)
+
+        self.assertEqual(1, len(children_of_type))
+        self.assertEqual(loaded_atom[0], children_of_type[0])
+
+    def testGetDescendantsOfType(self):
+        loaded_atom = atom.Atom(self.atom_stream)
+        descendants_of_type = loaded_atom.get_descendants_of_type(self.child_1_1_type)
+
+        self.assertEqual(3, len(descendants_of_type))
+        self.assertEqual(loaded_atom[0][0], descendants_of_type[0])
+        self.assertEqual(loaded_atom[0][1], descendants_of_type[1])
+        self.assertEqual(loaded_atom[1], descendants_of_type[2])
+
+
 
 class LoadedContainerAtomChildManipulation(unittest.TestCase):
     type = 'moov'