Discern which elements of a tree are leafs and which are nodes, given only preorder and postorder traversals

label.py

print """Sample tree:
           _1_
          / | \\
         2  3  4
           / \\  \\
          5   6  7
         / \\   \\
        8   9  10
"""

preorder = [1, 2, 3, 5, 8, 9, 6, 10, 4, 7]
postorder = [2, 8, 9, 5, 10, 6, 3, 7, 4, 1]
label = [None]*11

p = 0
r = 0
while None in label[1:]:
    while label[postorder[p]] is not None:
        p += 1
    label[postorder[p]] = "Leaf"
    q = preorder.index(postorder[p])
    while r < q:
        if label[preorder[r]] is None:
            label[preorder[r]] = "Node"
        r += 1

for i in range(1, 11):
    print i, label[i]

output.txt

Sample tree:
           _1_
          / | \
         2  3  4
           / \  \
          5   6  7
         / \   \
        8   9  10

1 Node
2 Leaf
3 Node
4 Node
5 Node
6 Node
7 Leaf
8 Leaf
9 Leaf
10 Leaf