Python处理文本文件键值对的两类技术问题求助

问题一：登录匹配成功后终止循环 #

当前登录代码会遍历文件所有行，即便找到匹配的用户仍会继续循环，且每一行不匹配时都会打印错误信息，逻辑不合理。以下是修正方案：

修正思路 #

1. 找到匹配的用户名和密码后，执行对应角色函数，立即终止循环并返回，避免无效遍历。
2. 不在循环内逐行打印错误，仅当遍历完所有行都未找到匹配项时，再统一提示用户名或密码错误。

修正后的代码 #

import ast

def login(userinput, passinput):
    login_db = "login.txt"
    found_user = False
    with open(login_db, 'r') as f:
        for single_line in f:
            try:
                dict_to_check = ast.literal_eval(single_line)
                username = dict_to_check['Username']
                password = dict_to_check['Password']
                role = dict_to_check['Role']

                if userinput == username:
                    found_user = True
                    if passinput == password:
                        if role == 'Immigration officer':
                            Immigration()
                        elif role == 'Customs officer':
                            Customs()
                        else:
                            print('Incorrect role you do not have the authority.')
                        # 匹配成功，终止循环
                        return
                    else:
                        print('Password is incorrect.')
                        # 用户名匹配但密码错误，无需继续遍历
                        return
            except Exception as e:
                print(f"An exception occurred: {e}")
    # 遍历完所有行未找到匹配用户名
    if not found_user:
        print('Incorrect username')

问题二：修改乘客文件中的Status值 #

文本文件无法直接修改单行内容，需先将所有数据读取到内存，修改对应项后再重新写入文件。

修正思路 #

1. 读取文件所有行，转换为字典列表存储。
2. 找到目标Civil ID对应的字典，修改其Status值。
3. 将修改后的字典列表重新写入原文件。

修正后的代码 #

import ast

def Existing_passenger(ID):
    passenger_db = "passenger.txt"
    # 读取所有乘客数据到内存
    passengers = []
    with open(passenger_db, 'r') as f:
        for single_line in f:
            try:
                passenger_dict = ast.literal_eval(single_line)
                passengers.append(passenger_dict)
            except Exception as e:
                print(f"An exception occurred when reading data: {e}")

    # 查找并修改目标乘客的Status
    updated = False
    for idx, p in enumerate(passengers):
        try:
            if p['Civil ID'] == ID:
                print("-Passenger's information-")
                print(f'Name: {p["Name"]}\nDate of birth: {p["DOB"]}\nGender: {p["Gender"]}\nCustoms fine: {p["Customs fine"]}\nStatus: {p["Status"]}\n')
                print('A. Arrival Approved\nB. Arrival Rejected\nC. Departure Approved\nD. Departure Rejected\nE. Go Back to previous menu')
                status_input = input('Select one of the following options: ')

                if status_input == 'A':
                    if p['Status'] == '':
                        p['Status'] = 'Arrival Approved'
                        updated = True
                elif status_input == 'B':
                    p['Status'] = 'Arrival Rejected'
                    updated = True
                elif status_input == 'C':
                    p['Status'] = 'Departure Approved'
                    updated = True
                elif status_input == 'D':
                    p['Status'] = 'Departure Rejected'
                    updated = True
                elif status_input == 'E':
                    print('Returning to previous menu...')
                    return
                else:
                    print('Wrong entry, please try again.')
                    Existing_passenger(ID)
                    return
                break
        except Exception as e:
            print(f"An exception occurred: {e}")

    # 将修改后的数据写回文件
    if updated:
        with open(passenger_db, 'w') as f:
            for passenger in passengers:
                f.write(f"{passenger}\n")
        print('Passenger status updated successfully.')
    else:
        print('No passenger found with the given Civil ID.')

额外提示 #

• 用ast.literal_eval解析字典字符串可行，但如果文件格式标准化，更推荐使用JSON格式（将单引号改为双引号），通过json模块读写，安全性和兼容性更强。
• 避免使用空except捕获所有异常，建议捕获具体异常类型（如SyntaxError、KeyError），便于排查问题。

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