gistfile1.py

from collections import namedtuple

def flatten(xs):
    return sum(xs, [])

Node = namedtuple('Node', 'value children')

def leaf(name):
    return Node(name, [])

tree1 = Node('e', [leaf('a'), leaf('b')])
tree2 = Node('f', [leaf('c'), leaf('d')])
tree3 = Node('i', [tree1, tree2])
tree4 = Node('j', [leaf('g'), leaf('h')])
tree = Node('k', [tree3, tree4])

def tree_walk_depth(tree):
    return [tree.value] + flatten(map(tree_walk_depth, tree.children))

def tree_walk_depend(tree):
    return flatten(map(tree_walk_depend, tree.children)) + [tree.value]

print(tree_walk_depth(tree))
print(tree_walk_depend(tree))