text: # chromosome.py
  # From Classic Computer Science Problems in Python Chapter 5
  # Copyright 2018 David Kopec
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  # http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  from __future__ import annotations
  from typing import TypeVar, Tuple, Type
  from abc import ABC, abstractmethod
  
  T = TypeVar("T", bound="Chromosome")  # for returning self
  
  
  # Base class for all chromosomes; all methods must be overridden
  class Chromosome(ABC):
      @abstractmethod
      def fitness(self) -> float:
          ...
  
      @classmethod
      @abstractmethod
      def random_instance(cls: Type[T]) -> T:
          ...
  
      @abstractmethod
      def crossover(self: T, other: T) -> Tuple[T, T]:
          ...
  
      @abstractmethod
      def mutate(self) -> None:
          ...
  