Python待办事项程序报错：列表字符串拼接类型错误及换行符去除需求

问题点 #

1. 运行代码时触发TypeError，错误行是print("here is you existing todo", todos + '\n')，报错信息：can only concatenate list (not "str") to list（无法将列表与字符串拼接）
2. 需要移除列表元素末尾的\n（例如将human\n转换为human）

错误回溯：

Traceback (most recent call last):
  File "C:\Users\awani\PycharmProjects\pythonProject\main.py", line 28, in <module>
    print("here is you existing todo", todos + '\n')
                                       ~~~~~~^~~~~~
TypeError: can only concatenate list (not "str") to list

修复步骤 #

1. 解决TypeError错误

todos是file.readlines()返回的列表类型，不能直接和字符串'\n'做拼接操作。要正确打印现有待办项，需要先把列表元素处理成可读的字符串：

• 遍历列表，用strip()去掉每个元素的换行符
• 用'\n'把处理后的元素连接成一个完整字符串
• 再打印输出

把错误行替换为：

formatted_todos = '\n'.join([item.strip() for item in todos])
print("here is your existing todo:\n", formatted_todos)

（顺便修正了原文的拼写错误：you → your）

2. 统一处理元素的换行符

建议在读取文件时就统一去掉所有元素的换行符，后续写入文件时再添加，避免重复处理：
把所有读取文件的代码：

todos = file.readlines()

替换为：

todos = [item.strip() for item in file.readlines()]

这样后续添加新待办项时，只需要在输入内容后拼接'\n'再写入文件即可。

修改后的完整代码 #

while True:
    user_action = input("Type add,show,exit,edit,complete: ")
    user_action = user_action.strip()

    if 'add' in user_action:
        todo_content = user_action[4:].title()
        with open('todos.txt', 'r') as file:
            todos = [item.strip() for item in file.readlines()]

        todos.append(todo_content)
        with open('todos.txt', 'w') as file:
            # 写入时统一添加换行符
            file.writelines([item + '\n' for item in todos])

    elif 'show' in user_action:
        with open('todos.txt', 'r') as file:
            todos = [item.strip() for item in file.readlines()]

        for index, item in enumerate(todos):
            row = f"{index + 1}-{item}"
            print(row)
    elif 'edit' in user_action:
        user_input = int(user_action[5:])
        user_value = user_input - 1
        
        with open('todos.txt', 'r') as file:
            todos = [item.strip() for item in file.readlines()]
        
        # 修复打印逻辑
        formatted_todos = '\n'.join(todos)
        print("here is your existing todo:\n", formatted_todos)

        todos[user_value] = input("Enter a new todo:").title()
        with open('todos.txt', 'w') as file:
            file.writelines([item + '\n' for item in todos])
    elif 'complete' in user_action:
        user_input = int(input("Enter a number to complete todo: "))
        with open('todos.txt', 'r') as file:
            todos = [item.strip() for item in file.readlines()]
        
        index = user_input - 1
        todo_to_remove = todos[index]

        todos.pop(index)
        with open('todos.txt', 'w') as file:
            file.writelines([item + '\n' for item in todos])
        
        message = f"This todo will be removed:{todo_to_remove}"
        print(message)
    elif 'exit' in user_action:
        print("Bye!")
        break
    else:
        print("Check and type again ")
print("Bye !")

内容的提问来源于stack exchange，提问作者Devil Is Dead