Python中给Employee类添加多个Course实例显示异常求助

定义了Course类和Employee类，给Employee实例添加单个Course时能正常显示课程名称，但添加第二个时，输出的是<__main__.Course object at 0x...>这类对象内存地址，而非期望的课程名称列表。

相关代码、当前输出及期望输出如下：

原代码 #

class Course:
    def __init__ (self, title, day, start, end):
        self.title = title
        self.day = day
        self.start = start
        self.end = end

    def __str__ (self):
        res = str(self.title)
        return res

class Employee:
    def __init__(self, firstn, lastn, DoB):
        self.firstn = firstn
        self.lastn = lastn
        self.DoB = DoB
        self.courses = "no courses"

    def add_course (self, course):
        if self.courses == "no courses":
            self.courses = course
        else:
            self.courses = self.courses, course

    def __str__ (self):
        res = str(self.firstn) + " " + str(self.lastn) + ", "
        res += "born " + str(self.DoB) + ", "
        res += "teaches " + str(self.courses)
        return res

if __name__ == "__main__":
    print("Create employee 'John Doe', born January 1st, 1990")
    john = Employee('John', 'Doe', '1990-01-01')
    print('  Created:', john)
    
    print("Create employee 'Jane Doe', born August 10, 1992")
    jane = Employee('Jane', 'Doe', '1992-08-10')
    print('  Created:', jane)
    
    print("Add 'Python I' to John Doe's courses")
    python1 = Course('Python I', 'Tuesday', 12, 14)
    john.add_course(python1)
    print('  John:', john)
    
    print("Add 'Introduction to Semantics' to John Doe's courses")
    semantics = Course('Introduction to Semantics', 'Monday', 10, 12)
    john.add_course(semantics)
    print('  John:', john)
    
    print("Add 'Python I' to Jane Doe's courses")
    jane.add_course(python1)
    print('  Jane:', jane)

当前输出 #

Create employee 'John Doe', born January 1st, 1990

  Created: John Doe, born 1990-01-01, teaches no courses

Create employee 'Jane Doe', born August 10, 1992

  Created: Jane Doe, born 1992-08-10, teaches no courses

Add 'Python I' to John Doe's courses

  John: John Doe, born 1990-01-01, teaches Python I

Add 'Introduction to Semantics' to John Doe's courses

  John: John Doe, born 1990-01-01, teaches (<__main__.Course object at 0x0000029B89DF0E10>, <__main__.Course object at 0x0000029B89DF0E50>)

Add 'Python I' to Jane Doe's courses

  Jane: Jane Doe, born 1992-08-10, teaches Python I

期望输出 #

John: John Doe, born 1990-01-01, teaches Python I, Introduction to Semantics

解决方案 #

问题根源在add_course方法：你将courses从单个Course对象转为了元组，而元组的默认字符串表示会显示元素的repr（即内存地址格式），而非调用每个元素的__str__。后续添加课程还会生成嵌套元组，逻辑更混乱。

正确做法是用列表统一管理课程，修改如下：

1. 修改Employee初始化逻辑 #

将self.courses = "no courses"改为空列表，统一用列表存储课程：

def __init__(self, firstn, lastn, DoB):
    self.firstn = firstn
    self.lastn = lastn
    self.DoB = DoB
    self.courses = []  # 初始化空列表表示无课程

2. 简化add_course方法 #

直接向列表追加课程，无需判断初始状态：

def add_course(self, course):
    self.courses.append(course)

3. 调整Employee的__str__方法 #

根据列表是否为空，生成对应的显示文本：

def __str__(self):
    res = f"{self.firstn} {self.lastn}, born {self.DoB}, teaches "
    if not self.courses:
        res += "no courses"
    else:
        res += ", ".join(str(course) for course in self.courses)
    return res

修改后的完整代码 #

class Course:
    def __init__ (self, title, day, start, end):
        self.title = title
        self.day = day
        self.start = start
        self.end = end

    def __str__ (self):
        return str(self.title)

class Employee:
    def __init__(self, firstn, lastn, DoB):
        self.firstn = firstn
        self.lastn = lastn
        self.DoB = DoB
        self.courses = []

    def add_course(self, course):
        self.courses.append(course)

    def __str__(self):
        res = f"{self.firstn} {self.lastn}, born {self.DoB}, teaches "
        if not self.courses:
            res += "no courses"
        else:
            res += ", ".join(str(course) for course in self.courses)
        return res

if __name__ == "__main__":
    print("Create employee 'John Doe', born January 1st, 1990")
    john = Employee('John', 'Doe', '1990-01-01')
    print('  Created:', john)
    
    print("Create employee 'Jane Doe', born August 10, 1992")
    jane = Employee('Jane', 'Doe', '1992-08-10')
    print('  Created:', jane)
    
    print("Add 'Python I' to John Doe's courses")
    python1 = Course('Python I', 'Tuesday', 12, 14)
    john.add_course(python1)
    print('  John:', john)
    
    print("Add 'Introduction to Semantics' to John Doe's courses")
    semantics = Course('Introduction to Semantics', 'Monday', 10, 12)
    john.add_course(semantics)
    print('  John:', john)
    
    print("Add 'Python I' to Jane Doe's courses")
    jane.add_course(python1)
    print('  Jane:', jane)

修改后的输出 #

Create employee 'John Doe', born January 1st, 1990
  Created: John Doe, born 1990-01-01, teaches no courses
Create employee 'Jane Doe', born August 10, 1992
  Created: Jane Doe, born 1992-08-10, teaches no courses
Add 'Python I' to John Doe's courses
  John: John Doe, born 1990-01-01, teaches Python I
Add 'Introduction to Semantics' to John Doe's courses
  John: John Doe, born 1990-01-01, teaches Python I, Introduction to Semantics
Add 'Python I' to Jane Doe's courses
  Jane: Jane Doe, born 1992-08-10, teaches Python I

内容的提问来源于stack exchange，提问作者user11579493