Fixing node_number_at_depth for empty trees.

sagemath · Feb 2, 2020 · aaa0581 · aaa0581
1 parent 87c3057
commit aaa0581
Showing 1 changed file with 14 additions and 0 deletions.
diff --git a/src/sage/combinat/abstract_tree.py b/src/sage/combinat/abstract_tree.py
@@ -822,7 +822,21 @@ def node_number_at_depth(self, depth):
                    o
             sage: [T.node_number_at_depth(i) for i in range(6)]
             [1, 3, 4, 2, 1, 0]
+
+        TESTS:
+
+        Check that the empty tree has no nodes (:trac:`29134`)::
+
+            sage: T = BinaryTree()
+            sage: T
+            .
+            sage: T.is_empty()
+            True
+            sage: [T.node_number_at_depth(i) for i in range(3)]
+            [0, 0, 0]
         """
+        if self.is_empty():
+            return Integer(0)
         if depth == 0:
             return Integer(1)
         return sum(son.node_number_at_depth(depth - 1) for son in self)