text: import random
  import string
  
  
  def random_string_generator(size=10, chars=string.ascii_lowercase + string.digits):
      return ''.join(random.choice(chars) for _ in range(size))
  
  
  def unique_order_id_generator(instance):
      new_bill_id= random_string_generator()
  
      Klass= instance.__class__
  
      qs_exists= Klass.objects.filter(bill_id= new_bill_id).exists()
      if qs_exists:
          return unique_order_id_generator(instance)
      return new_bill_id
  