How to Persist User Data in Python Without Overwriting Existing Dictionaries

Introduction: The author, a Python enthusiast, received a question about how to add data to existing keys in a dictionary without recreating it each run.

Implementation Process

The solution modifies existing code to load data from a JSON file, append new usernames, emails, and passwords while avoiding duplicates, and then write the updated data back to the file.

import json

def load_data():
    try:
        with open('user.json', 'r', encoding='utf-8') as f:
            return json.load(f)
    except FileNotFoundError:
        return {
            "用户名": [],
            "密码": [],
            "邮箱": []
        }

def login(data):
    print("欢迎来到图书管理系统注册页面~")
    while True:
        username = input("请输入用户名:\t")
        if len(username) < 5:
            print("用户名不能小于5位")
        else:
            if username not in data["用户名"]:
                data["用户名"].append(username)
                email = input("请输入邮箱:\t")
                if email.endswith('@zxs.com'):
                    if email not in data["邮箱"]:
                        data["邮箱"].append(email)
                        password = input("请输入密码:\t")
                        if len(password) >= 6:
                            data["密码"].append(password)
                            print(f"Tips: 恭喜{username}注册成功,请前往登录")
                            save(data)
                            break
                        else:
                            print("密码不能小于6位")
                    else:
                        print("邮箱已存在，请使用其他邮箱注册")
                else:
                    print("邮箱格式错误,邮箱后缀必须是@zxs.com")
            else:
                print("用户名已存在，请使用其他用户名注册")

def save(data):
    try:
        with open('user.json', 'w', encoding='utf-8') as f:
            json.dump(data, f, ensure_ascii=False, indent=4)
    except Exception as e:
        print("文件写入失败,请检查文件路径")

if __name__ == '__main__':
    data = load_data()
    login(data)

Conclusion: The script successfully resolves the original problem, showing how to persist user information in a JSON file while preventing duplicate entries.