Detect cycle in a directed graph

detect.py

#
  # detect cycle
  # in a directed graph 
  # sadi304
#

def dfs(G, u, color, found_cycle):
  if found_cycle[0]:
    return
  color[u] = "gray"
  for v in G[u]:
    if color[v] == "gray": 
      found_cycle[0] = True       
      return
    if color[v] == "white": 
      dfs(G, v, color, found_cycle)
  color[u] = "black" 

def cycleCheck(G):
  color = { u : "white" for u in G  } # mark as white, that is: inititally nodes are not visited
  found_cycle = [False]
  for u in G:
    if color[u] == "white":
      dfs(G, u, color, found_cycle)
    if found_cycle[0]:
      break
  return found_cycle[0]

graphWithCycle = { 
  0: [1],
  1: [2],
  2: [3],
  3: [4],
  4: [5],
  5: [3] 
}

hasCycle = cycleCheck(graphWithCycle)

print(hasCycle)