Python循环读取外部文件时else语句重复输出的问题及解决

• 现有两个文件：外部文件tasks.txt和主文件task_manager.py
• tasks.txt的单行内容格式示例：
  admin, Register Users with taskManager.py, Use taskManager.py to add the usernames and passwords for all team members that will be using this program., 10 Oct 2019, 20 Oct 2019, No
• 字段含义（以逗号加空格分隔）：用户名、任务标题、任务描述、分配日期、截止日期、任务完成状态

需求：读取tasks.txt，当用户名匹配时按指定格式打印对应行；无匹配用户名时，仅打印一次You have no tasks at the moment。

初始代码使用for循环读取文件时，else语句会针对tasks.txt的每一行重复输出提示信息，代码如下：

username = "admi"

f2 = open('tasks.txt', 'r')

for line in f2:
    line3_split = line.split(', ')
    if line3_split[0] == username:
        user_format = f"""
        Task:              {line3_split[1]}
        Assigned to:       {line3_split[0]}
        Date assigned:     {line3_split[3]}
        Due date:          {line3_split[4]}
        Task complete?     {line3_split[5]}
        Task description:  
         {line3_split[2]}
        """
        print(user_format)
    else:
        print("You have no tasks at the moment.")


f2.close()

修改代码先判断用户名是否存在于文件内容中，解决了重复输出问题，但for循环失效——原因是文件读取一次后指针停在末尾，无法再次读取。修改后的代码：

username = "admn"

f2 = open('tasks.txt', 'r')

is_user = f2.read()

if username in is_user:
    for line in f2:
        line3_split = line.split(', ')
        if line3_split[0] == username:
            user_format = f"""
            Task:              {line3_split[1]}
            Assigned to:       {line3_split[0]}
            Date assigned:     {line3_split[3]}
            Due date:          {line3_split[4]}
            Task complete?     {line3_split[5]}
            Task description:  
            {line3_split[2]}
            """
            print(user_format)
else:
    print("You have no tasks at the moment.")

f2.close()

使用.seek(0,0)重置文件指针到文件开头，实现二次读取文件，解决所有问题。最终代码：

username = "admin"

f2 = open('tasks.txt', 'r')

is_user = f2.read()

if username in is_user:
    f2.seek(0,0)
    for line in f2:
        line3_split = line.split(', ')
        if line3_split[0] == username:
            user_format = f"""
            Task:              {line3_split[1]}
            Assigned to:       {line3_split[0]}
            Date assigned:     {line3_split[3]}
            Due date:          {line3_split[4]}
            Task complete?     {line3_split[5]}
            Task description:  
             {line3_split[2]}
            """
            print(user_format)
else:
    print("You have no tasks at the moment.")

f2.close()

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