text: import inspect
  import sys
  from typing import Dict, List, Type
  
  
  RegisterType = Dict[int, List[int]]
  
  class UserModel:
  
      Users = []
  
      def __init__(self, customer_id: int):
          self.customer_id = customer_id
          self.items = []
  
          UserModel.Users.append(self)
  
  
      def add_item(self, item_id: int):
          self.items.append(item_id)
  
  
      @classmethod
      def FindUserByCustomer_id(cls, customer_id):
          for x in cls.Users:
              if customer_id == x.customer_id:
                  return x
          return None
  
  
      @classmethod
      def deleteUser(cls, customer_id: int):
          user = cls.FindUserByCustomer_id(customer_id)
          cls.Users.remove(user)
  
      @classmethod
      def clear(cls):
          cls.Users = []
  
  
      def __repr__(self):
          return f"'{self.customer_id}', {self.items})"
  
  
  
  class BaseModel:
      """
      Base class for creating other models.
      """
  
      def __init__(self, register_count: int):
          self.register_count = register_count
          self.registers: RegisterType = {i: [] for i in range(self.register_count)}
  
          #self.customer_register_assignments: Dict[int, int] = {}
  
      def clear(self):
          self.registers = {i: [] for i in range(self.register_count)}
          UserModel.clear()
  
  
      def _select_register(self) -> int:
  
          minUsersInRegister = 100 # Or max number allowed in memory
          tempMin = minUsersInRegister
          register = -1
  
          for reg in self.registers:
              minUsersInRegister = min(minUsersInRegister, len(self.registers[reg]))
  
              if minUsersInRegister < tempMin:
                  tempMin = minUsersInRegister
                  register = reg
  
  
  
          return register
  
  
      def _remove_user_from_register(self, customer_id: int):
          """
          Select a register to use for new customers.
          """
  
          for _, value in self.registers.items():
              count = 0
              for item in value:
                  if item["customer_id"] == customer_id:
                          value.pop(count)
                          break
                  count += 1
  
  
  
  
      def add(self, customer_id: int, item_id: int):
  
          user = UserModel.FindUserByCustomer_id(customer_id)
          """
              - If the customer is new, select a register using the model.
          """
          if user is None:
              user = UserModel(customer_id)
              user.add_item(item_id)
              user_object = {"customer_id": user.customer_id, "items": user.items}
  
              register = self._select_register()
              self.registers[register].append(user_object)
  
          else:
              """
              Add an item to a register using the following rules:
                  - If the customer already has items on a register, select that register.
              """
              user.add_item(item_id)
  
  
  
  
  
      def checkout(self, customer_id: int):
          """
          Clear the customer's register assignment and remove their items from the register.
          """
  
          user = UserModel.FindUserByCustomer_id(customer_id)
  
          if user:
              UserModel.deleteUser(customer_id)
              self._remove_user_from_register(customer_id)
  
  
          # return self.registers
          # raise NotImplementedError()
  
  
      def __repr__(self):
          return f"'{self.register_count}', {self.registers})"
  
  
      @staticmethod
      def get_model(model_name: str) -> Type["BaseModel"]:
          """
          Search this module for a subclass of BaseModel with a name that matches the given model name.
          """
          matches = (
              cls
              for name, cls in inspect.getmembers(
                  object=sys.modules[__name__], predicate=inspect.isclass
              )
              if issubclass(cls, BaseModel) and name == model_name
          )
          cls = next(matches, None)
          if not cls:
              raise TypeError(f"{model_name} is not a subclass of BaseModel or it does not exist.")
          return cls