用户名和密码注册、登陆系统，SQLite数据库版本

import hashlib
import pickle, os
import hmac, random
import sqlite3


def hmac_sha1(key, s):
    return hmac.new(key.encode('utf-8'), s.encode('utf-8'), 'MD5').hexdigest()


conn = sqlite3.connect('user.db')
cursor = conn.cursor()
try:
    cursor.execute('create table userpass (name varchar(20) primary key, password varchar(20))')
except Exception as e:
    pass

# 创建或者连接数据库
# conn = sqlite3.connect('user.db')
# cursor = conn.cursor()
# try:
#     cursor.execute('create table userpass (name varchar(20), password varchar(20))')
# except Exception as e:
#     print('Error: ', e)

# 获取用户名和密码信息
# if os.path.exists('/Users/lewisliu/user_information.txt'):
#     with open('/Users/lewisliu/user_information.txt', 'rb') as f:
#         user_information = pickle.load(f)
# else:
#     user_information = dict()

# 注册或者登陆
while True:
    # conn = sqlite3.connect('user.db')
    # cursor = conn.cursor()
    # try:
    #     cursor.execute('create table userpass (name varchar(20) primary key, password varchar(20))')
    # except Exception as e:
    #     pass
        # print('Error: ', e)

    # 选择模式，注册、登陆、退出
    model = input("pleas input enroll/login/exit:")
    if model == 'enroll':
        name = input("please input your name:")
        # 用户名重复识别
        flag = cursor.execute("select name from userpass where name='%s'" % name).fetchone()
        if flag:
            print('name is exist!')
        else:
            password = input("please input your password:")
            key = 'liu'  # ''.join([chr(random.randint(48, 122)) for i in range(20)])
            password = hmac_sha1(key, password)
            cursor.execute("insert into userpass (name, password) values ('%s','%s')" % (name, password))
            conn.commit()
            # conn.close()
        # if name in user_information.keys():
        #     print("name is occupied!")
        #     continue
        # password = input("please input your password:")
        # # 数据库添加用户名和密码
        # key = 'liu' # ''.join([chr(random.randint(48, 122)) for i in range(20)])
        # user_information[name] = hmac_sha1(key, password)
        # sha1 = hashlib.sha1()
        # sha1.update(password.encode('utf-8'))
        # user_information[name] = sha1.hexdigest()
    elif model == 'login':
        name = input("please input your name:")
        flag = cursor.execute("select name from userpass where name='%s'" % name).fetchone()
        if flag:
            password = input("please input your password:")
            key = 'liu'
            password = hmac_sha1(key, password)
            flag = cursor.execute("select name and password from userpass where name = '%s' and password='%s'" % (name, password)).fetchone()
            if flag:
                print("Wellcome!")
            else:
                print("wrong password! Exit!")
                conn.close()
                exit()
        else:
            print("name is not exist!")
        # if name not in user_information.keys():
        #         #     print("name is not exist!")
        #         #     continue
        #         # password = input("please input your password:")
        #         # key = 'liu' # ''.join([chr(random.randint(48, 122)) for i in range(20)])
        #         # password = hmac_sha1(key, password)
        #         # # sha1 = hashlib.sha1()
        #         # # sha1.update(password.encode('utf-8'))
        #         # # password = sha1.hexdigest()
        #         # if user_information[name] == password:
        #         #     print("Wellcome!")
        #         # else:
        #         #     print("wrong name or password! Exit!")
        #         #     with open('/Users/lewisliu/user_information.txt', 'wb') as f:
        #         #         pickle.dump(user_information, f)
        #         #     exit()
    elif model == 'exit':
        conn.close()
        exit()
        # with open('/Users/lewisliu/user_information.txt', 'wb') as f:
        #     pickle.dump(user_information, f)
        # exit()
    else:
        print("model wrong!")