如何從Python的遞歸函數返回列表？

Question

我有以下代碼：

def primes(n):
  acc = []
  return do_primes(range(2,n,1), acc)

def do_primes(xs, acc):
  if xs:
    head, tail = xs[0], xs[1:]
    acc.append(head)
    do_primes([x for x in xs if x % head != 0], acc)
  else:
    return acc

調用代碼將輸出為None：

>>> primes(10)
None

Answer 1

您需要再次return ：

def do_primes(xs, acc):
  if xs:
    head, tail = xs[0], xs[1:]
    acc.append(head)
    return do_primes([x for x in xs if x % head != 0], acc)
  else:
    return acc