finnish_vatnum_check.py

def is_vatnum(num):
  if len(num) > 9:
    return False

  if "-" not in num:
    return False

  n,check = num.split("-")

  try:
    int(n)
  except:
    return False

  try:
    check = int(check)
  except:
    return False

  multips = [7, 9, 10, 5, 8, 4, 2]

  if len(n) != len(multips):
    return False

  control_sum = 0
  for idx, mnum in enumerate(multips):
    nnum = int(n[idx])
    control_sum += nnum * mnum

  control_sum %= 11

  if control_sum == 0:
    return check == control_sum
  elif control_sum >= 2 and control_sum <= 10:
    return (11 - control_sum) == check

  return False