input: 
  import random 
  
  def generate_number() -> int:
      """ Generate a unique 6 digit number.
      >>> generate_number()
      12345
      >>> generate_number()
      54321
      """
      random_number = random.randint(10000, 99999)
      return random_number
  
output:     while True:
          if str(random_number) not in generated_numbers:
              generated_numbers.add(str(random_number))
              return random_number
          random_number = random.randint(10000, 99999)