Simple depth-first searcher in Python 2.7

depth-first-search.py

'''
Depth-first searcher

Tree:
    a
   / \
  b   c
 /|\   \
d e f   g
        |
        h
'''

tree = {
    'a': ['b', 'c'],
    'b': ['d', 'e', 'f'],
    'c': ['g'],
    'g': ['h'],
}


# Depth first search with stack
def dfs(tree, target, start):
    stack = [start]
    visited = set()
    while stack:
        if stack[-1] == target:
            return target
        visited.add(stack[-1])
        children = tree[stack[-1]] if stack[-1] in tree else []
        new_child = None
        for child in children:
            if child not in visited:
                new_child = child
                break
        if new_child:
            stack.append(new_child)
        else:
            stack.pop(-1)
    return None

start = 'a'
test_set = ['a', 'b', 'c', 'f', 'g', 's']
for t in test_set:
    print "DFS searching", t, ':', dfs(tree, t, start)