Recursive subtree check

subtree.py

def contains_tree(a,b):
    if b is None:
        #an empty child tree is always a subtree
        return True
    return sub_tree(a,b)

def sub_tree(a,b):
    if a is None:
        #if larger tree is exhausted, return false
        return False
    if a == b:
        #if matching point is found, check descending data
        if match_tree(a,b): return True
        
    #recurse until any matches are found
    return sub_tree(a.left,b) or sub_tree(a.right,b)

def match_tree(a,b):
    if b is None and a is None:
        #if match is exhaustive on both trees, the subtree
        #and parent terminate with the same vals
        return True

    if a is None or b is None:
        #if only one tree exhausts, cannot be subtree
        return False

    if a != b:
        #if the data does not match, trees are different
        return False 
    #recursively match data on all descendents (both sides)
    return match_tree(a.left,b.left) and match_tree(a.right,b.right)

print contains_tree(tree_a.root,tree_b.root)