一、实践练习
练习1：图书管理系统
python
class Book:
"""图书类"""
def init(self, title, author, isbn):
self.title = title
self.author = author
self.isbn = isbn
self.is_borrowed = False
def borrow(self):if not self.is_borrowed:self.is_borrowed = Trueprint(f"《{self.title}》借阅成功")return Trueelse:print(f"《{self.title}》已被借出")return Falsedef return_book(self):if self.is_borrowed:self.is_borrowed = Falseprint(f"《{self.title}》归还成功")else:print(f"《{self.title}》未被借出")def __str__(self):status = "已借出" if self.is_borrowed else "可借"return f"《{self.title}》作者：{self.author} | 状态：{status}"
class Library:
"""图书馆类"""
def init(self, name):
self.name = name
self.books = []
def add_book(self, book):self.books.append(book)print(f"添加图书：{book.title}")def search_by_title(self, title):results = [book for book in self.books if title.lower() in book.title.lower()]return resultsdef show_all_books(self):if not self.books:print("图书馆暂无图书")else:print(f"\n{self.name}馆藏图书：")for i, book in enumerate(self.books, 1):print(f"{i}. {book}")
使用示例
lib = Library("社区图书馆")
book1 = Book("Python编程", "张三", "123")
book2 = Book("算法导论", "李四", "456")
book3 = Book("设计模式", "王五", "789")
lib.add_book(book1)
lib.add_book(book2)
lib.add_book(book3)
lib.show_all_books()
book1.borrow()
book1.borrow() # 尝试再次借阅
book1.return_book()
print("\n搜索'python'😊
for book in lib.search_by_title("python"):
print(book)
练习2：员工薪资系统（继承应用）
python
class Employee:
"""员工基类"""
def init(self, emp_id, name, base_salary):
self.emp_id = emp_id
self.name = name
self.base_salary = base_salary
def calculate_salary(self):"""计算工资，子类应重写"""return self.base_salarydef get_info(self):return f"工号：{self.emp_id} | 姓名：{self.name}"
class Manager(Employee):
"""经理类"""
def init(self, emp_id, name, base_salary, bonus_rate=0.2):
super().init(emp_id, name, base_salary)
self.bonus_rate = bonus_rate
def calculate_salary(self):return self.base_salary * (1 + self.bonus_rate)def get_info(self):return super().get_info() + " | 职位：经理"
class Salesperson(Employee):
"""销售员类"""
def init(self, emp_id, name, base_salary, sales_amount=0):
super().init(emp_id, name, base_salary)
self.sales_amount = sales_amount
self.commission_rate = 0.1
def calculate_salary(self):return self.base_salary + self.sales_amount * self.commission_ratedef get_info(self):return super().get_info() + f" | 职位：销售员 | 销售额：{self.sales_amount}"
class Developer(Employee):
"""开发工程师类"""
def init(self, emp_id, name, base_salary, project_count=0):
super().init(emp_id, name, base_salary)
self.project_count = project_count
def calculate_salary(self):return self.base_salary + self.project_count * 2000def get_info(self):return super().get_info() + f" | 职位：开发工程师 | 项目数：{self.project_count}"
多态应用
employees = [
Manager("M001", "张经理", 10000),
Salesperson("S001", "李销售", 3000, 50000),
Developer("D001", "王开发", 8000, 3)
]
total_salary = 0
print("=== 员工工资明细 ===")
for emp in employees:
salary = emp.calculate_salary()
total_salary += salary
print(f"{emp.get_info()} | 本月工资：{salary:.2f}元")
print(f"\n总工资支出：{total_salary:.2f}元")
练习3：自定义异常类
python
class AgeError(Exception):
"""自定义异常：年龄不合法"""
pass
class Person:
def init(self, name, age):
self.name = name
self.set_age(age) # 通过方法设置年龄
def set_age(self, age):if not isinstance(age, int):raise TypeError("年龄必须是整数")if age < 0 or age > 150:raise AgeError(f"年龄 {age} 不在有效范围(0-150)")self.__age = agedef get_age(self):return self.__age
测试自定义异常
try:
p1 = Person("小明", 20)
print(f"{p1.name}年龄：{p1.get_age()}")
p2 = Person("小红", 200) # 触发异常
except AgeError as e:
print(f"年龄错误：{e}")
except TypeError as e:
print(f"类型错误：{e}")
二、遇到的问题与解决
问题：忘记在方法定义中添加self参数
解决：实例方法的第一个参数必须是self，调用时自动传递
提示：TypeError: method() takes 0 positional arguments but 1 was given
问题：在类内部调用实例方法时忘记加self.
解决：必须使用self.方法名()调用同一类的其他实例方法
问题：私有属性名称改编规则不熟悉
解决：__attr被重命名为_ClassName__attr，尽量避免直接访问
问题：继承时子类未调用父类__init__
解决：使用super().init(参数)显式调用父类构造函数
后果：父类属性未初始化，导致子类对象缺少父类定义的属性
问题：类属性与实例属性同名时的查找顺序
解决：实例属性优先于类属性（实例.属性），类属性需要通过类名访问
学习总结
面向对象编程是一种强大的编程范式，将数据与操作封装在一起
类是创建对象的模板，__init__方法用于初始化对象状态
实例属性属于具体对象，类属性属于类本身（所有实例共享）
方法类型：实例方法、类方法、静态方法，各有用途
封装通过命名约定实现，Python不强制访问控制，但提供了_和__的约定
继承允许子类重用父类代码，方法重写实现多态
多态使得同一接口可以处理不同类型的对象，提高代码灵活性