用户名和密码验证在Python中可通过多种方式实现，以下是常见方法及示例代码：

一、简单验证（明文比对）

适用于教学或非敏感场景，直接将用户输入与预设密码对比。

users = { "alice": "password123", "bob": "secretpassword" }

def authenticate(username, password):
    return username in users and users[username] == password

username = input("请输入用户名: ")
password = input("请输入密码: ")
if authenticate(username, password):
    print("身份验证成功！")
else:
    print("身份验证失败。")

二、带锁定机制的验证

通过记录错误次数实现账户锁定，防止暴力破解。

# 锁定次数阈值
MAX_ATTEMPTS = 3

def authenticate(username, password):
    with open("login_lock.txt", "r") as f:
        locked_users = set(line.strip() for line in f)
    if username in locked_users:
        print("用户名已被锁定，请联系管理员。")
        return False

    with open("login.txt", "r") as f:
        for line in f:
            stored_username, stored_password = line.strip().split(":")
            if username == stored_username and password == stored_password:
                return True
    return False

username = input("请输入用户名: ")
password = input("请输入密码: ")
attempts = 0
while attempts < MAX_ATTEMPTS:
    if authenticate(username, password):
        print("欢迎使用系统！")
        break
    else:
        attempts += 1
        print(f"错误次数：{attempts}/{MAX_ATTEMPTS}，账户已被锁定。")

三、使用哈希和盐值保护密码

实际应用中，密码应加密存储，避免明文风险。

import hashlib
import os

# 假设用户数据存储在字典中
users = { "alice": "password123", "bob": "secretpassword" }

def hash_password(password):
    salt = os.urandom(16).hex()
    return hashlib.sha256((salt + password).encode()).hexdigest()

def authenticate(username, password):
    if username in users:
        stored_hash = users[username]
        return hash_password(password) == stored_hash
    return False

username = input("请输入用户名: ")
password = input("请输入密码: ")
if authenticate(username, password):
    print("登录成功！")
else:
    print("密码错误。")

四、结合文件读写的完整示例

实现注册、登录及锁定功能，适用于小型应用。

# 假设用户数据存储在login.txt文件中
def register(username, password):
    with open("login.txt", "a") as f:
        f.write(f"{username}:{hash_password(password)}\n")

def authenticate(username, password):
    with open("login.txt", "r") as f:
        for line in f:
            stored_username, stored_hash = line.strip().split(":")
            if username == stored_username and hash_password(password) == stored_hash: