Add feature get_parent_node.

binarytree/__init__.py

@@ -314,6 +314,57 @@ def _get_tree_properties(root):
     }
 
 
+def get_parent_node(root, node):
+    """Search from the binary tree and return the parent node for require node.
+
+    :param root: Root node of the binary tree.
+    :rtype: binarytree.Node
+    :param node: Require node you want to get its parent node.
+    :rtype: binarytree.Node
+    :return: The parent node of require node.
+    :rtype: binarytree.Node
+
+    **Example**:
+
+        .. doctest::
+
+            >>> from binarytree import Node, get_parent_node
+            >>> root = Node(0)
+            >>> root.left = Node(1)
+            >>> root.right = Node(2)
+            >>> root.left.left = Node(3)
+            >>> print (root)
+            >>>     0
+                   / \
+                  1   2
+                 /
+                3
+            >>> print (get_parent_node(root, root.left.left))
+            >>>   1
+                 /
+                3
+    """
+    if root is node or root is None or node is None:
+        return None
+    node_stack = []
+    while True:
+        if root is not None:
+            node_stack.append(root)
+            if root.left is node:
+                return root
+            else:
+                root = root.left
+        elif len(node_stack) > 0:
+            root = node_stack.pop()
+            if root.right is node:
+                return root
+            else:
+                root = root.right
+        else:
+            break
+    return None
+
+
 class Node(object):
     """Represents a binary tree node.
 

tests/test_tree.py

@@ -6,6 +6,7 @@
 import pytest
 
 from binarytree import Node, build, tree, bst, heap
+from binarytree import get_parent_node
 from binarytree.exceptions import (
     NodeValueError,
     NodeIndexError,
@@ -882,3 +883,18 @@ def test_heap_float_values():
             assert root.min_leaf_depth == root_copy.min_leaf_depth
             assert root.min_node_value == root_copy.min_node_value + 0.1
             assert root.size == root_copy.size
+
+
+@pytest.mark.order14
+def test_get_parent_node():
+    root = Node(0)
+    root.left = Node(1)
+    root.right = Node(2)
+    root.left.left = Node(3)
+    root.right.right = Node(4)
+    assert get_parent_node(root, root.left.left) == root.left
+    assert get_parent_node(root, root.left) == root
+    assert get_parent_node(root, root) is None
+    assert get_parent_node(root, root.right.right) == root.right
+    assert get_parent_node(root, root.right) == root
+    assert get_parent_node(root, Node(5)) is None