input: from typing import List
  
  def generate_unique_number(existing_numbers: List[int]) -> int:
      """ Generate a unique 6-digit number that is not in the list of existing numbers.
      >>> generate_unique_number([12345, 67890])
      98765
      >>> generate_unique_number([10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000])
      99999
      """
      while True:
          number = random.randint(100000, 999999)
          if number not in existing_numbers:
              return number
output:     import random