python - 递归 - Python - 为什么 print(Foo) 显示的内容与 print(FunctionReturningFoo()) 不同

Question

为什么 print(foo) 显示的内容与 print(functionreturningthesame()) 不同

查看输出，打印函数中的数组显示正确答案，但打印函数的返回结果却没有。我可能对递归迭代感到困惑......

def AreNotOpposite(a,b):
  if a == "NORTH" and b == "SOUTH":
    return False
  if a == "SOUTH" and b == "NORTH":
    return False
  if a == "WEST" and b == "EAST":
    return False
  if a == "EAST" and b == "WEST":
    return False
  return True

def canBeBetter(arr):
  for i in range(len(arr)-1):
    if not AreNotOpposite(arr[i],arr[i+1]):
      return True
  return False

def dirReduc(arr):
  re = []
  avoid = -1
  for i in range(len(arr)):
    if avoid == i:
      continue
    if i+1 == len(arr):
      re.append(arr[i])
    elif AreNotOpposite(arr[i],arr[i+1]):
      re.append(arr[i])
    else: #do not append neither the nextone
      avoid = i+1
  if canBeBetter(re):  #can reduce more?
    dirReduc(re)
  else:
    print(re)
    return re

print (dirReduc(['NORTH', 'WEST', 'EAST','SOUTH', 'NORTH','SOUTH','EAST','NORTH']))

输出:

['EAST', 'NORTH']
None

Answer 1

您需要返回递归调用的结果(否则您的函数将到达逻辑末尾并简单地返回None):

if canBeBetter(re):  #can reduce more?
  return dirReduc(re)
else:
  print(re)
  return re