dfs.py

gm = {0: [0, 1, 4], 1: [0, 2], 2: [3, 4], 3: [2, 1], 4: []}
g = lambda x: gm[x]

def dfs(graph, start, stack=None):
    if stack is None:
        stack = []
    if start in stack:
        print("Cycle detected involving:", start)
        return
    print("Visiting:", start)
    stack.append(start)
    for newStart in graph(start):
        dfs(graph, newStart, stack)
    print("Done with:", start)

dfs(g,0)