上回书说到，这两天突然闲着没事，想自己做一个数据库。

        上次是已经把登录系统做完了（见代码）：

import json#json解析
import os#数据读写，文件操作
import sys#控制退出
import time#控制暂停
import shutil#文件夹操作
 
 
 
def saveToJSON(dicObject,file):
    flag=False
    '''#这一段注释掉了，因为后面发现这样不能完全满足使用需求。
    if type(dicObject)!=dict:
        print('dict')
        return flag
    '''
    try:
        j_file=open("./PyDB/"+file,'a')#打开文件，PyDB是储存数据的文件夹，后面会说到
        json.dump(dicObject,j_file,ensure_ascii=False)#以JSON格式储存数据
        flag=True
    except:
        print('写数据出错!')
    finally:
        if flag:
            j_file.close()
    return flag
#=========================
def GetFromJSON(filename):
    flag=False
    dicObject={}
    try:
        way="./PyDB/"+filename#文件路径
        j_file=open(way,'r')#以只读方式打开文件
        dicObject=json.load(j_file)#使用json的load方法解析数据
        flag=True
    except:
        flag=False
    finally:
        if flag:
            j_file.close()
        elif flag==False:
            return False
    return dicObject



def turn(file):
    with open(file,mode='r',encoding='utf-8') as f:#用with语句打开文件
        a=f.readline()#将文件以字符串形式读出
        a=a.split('","')#以“，”为间隔，将字符串分割成表格
        b=[]#返回的列表
        for i in range(len(a)):
            if i <= len(a)-2:#a的结尾会有一个‘“，”’，需要把它去掉
                b.append(json.loads(a[i]))#用json解析字符串并添加到列表中
        return b




if __name__ == '__main__':
    print("| Welcome to PyDB Monitor.")#一些简要信息
    print("| Server version: 1.0.0 PyDB Server.")
    print("| Add '@' at the beginning of the statement.")
    print("| Type '@help' or '@h' for help.Type '@continue' or '@c' to clear the current input statement.\n")
    print("PyDB>Welcome to PyDB!"+"\n")#欢迎语句
    folder=''#判断是否存在数据库文件夹
    for i in range(len(os.listdir())):
        a=os.listdir()
        if a[i]=='PyDB':
            folder='PyDB'
    if folder!='PyDB':#如果没有，则创建数据库文件夹
        os.makedirs('./PyDB'+'./user')
        os.makedirs('./PyDB'+'./DataBase')


    #----------------------------------------------------登录
    while True:
 
        if len(os.listdir('./PyDB/user'))==0:#判断是否存在用户，如果没有，则创建一个超级管理员
            print("PyDB> There are no users yet :( ...  Let's create one! :) \n")
            admin=input("PyDB>  Please enter your User Name!\nAdministrator>")
            Pass=input("PyDB> Please enter your password!\nPassword>")
            RePass=input("PyDB> Please enter your password again!\nPassword>")
            if Pass==RePass:#判断两次输入的密码是否一致
                #用户信息
                info={
                    'Name':admin,'Password':Pass,'Jurisdiction':'Root'
                }
                saveToJSON(info,'user/'+admin+'.json')#储存信息
                print("\nSuccess>Congratulations, account creation succeeded!\n")
                host=GetFromJSON("user/"+admin+".json")#为后面的一些判断做准备
                os.makedirs('./PyDB'+'./DataBase'+'./'+admin)#在数据库文件夹下创建用户文件夹
                break#跳出循环，进行数据操作
            else:#不一致则进入另一个循环
                while True:
                    print('PyDB>The two passwords you entered are different. Please try again.')
                    Pass=input("PyDB> Please enter your password!\nPassword>")
                    RePass=input("PyDB> Please enter your password again!\nPassword>")
                    if Pass==RePass:
                        info={
                            'User':admin,'Password':Pass,'Jurisdiction':'Root'
                        }
                        saveToJSON(info,'user/'+admin+'.json')
                        print("\nSuccess>Congratulations, account creation succeeded!\n")
                        host=GetFromJSON("user/"+admin+".json")
                        os.makedirs('./PyDB'+'./DataBase'+'./'+admin)
                        break
                    break
        else:#如果存在用户，则进行登录操作
            while True:
                admin=input('User name>')
                if admin=="@exit":#若需退出，则可以在此退出
                    print("PyDB>Thank you for your use~ :) Bye!")
                    time.sleep(3)
                    sys.exit()
                if GetFromJSON("user/"+admin+".json")==False:#判断该用户是否存在
                    print("Error>Sorry, there is no such user.Please try again.")
                else:
                    host=GetFromJSON("user/"+admin+".json")#获取用户信息
                    break
            Pass=input('Password>')#用户密码
            if Pass=="@exit":#若需退出，则可以在此退出
                print("PyDB>Thank you for your use~ :) Bye!")
                time.sleep(3)
                sys.exit()
            if host["Password"]!=Pass:#若三次密码错误，则退出程序
                print("Error>Password error, please try again!")
                Pass=input('Password>')
                host=GetFromJSON("user/"+admin+".json")
                if host["Password"]!=Pass:
                    print("Error>Password error, please try again!")
                    Pass=input('Password>')
                    host=GetFromJSON("user/"+admin+".json")
                    if host['Password']!=Pass:
                        print("Error>You have made three consecutive errors. Please try again later.")
                        time.sleep(3)
                        sys.exit()
                    else:
                        print("\n"+"PyDB>Welcome,"+admin+'!\n')
                        break
                else:
                    print("\n"+"PyDB>Welcome,"+admin+'!\n')
                    break
            else:
                print("\n"+"PyDB>Welcome,"+admin+'!\n')
                break#进入操作界面

        那么今天，我们来做后面的数据操作系统！（即第二个大循环）

jurisdiction=host["Jurisdiction"]
    maindatabase=''

        这个“jurisdiction"就是用户的权限，这个在后面我们会用到（毕竟谁也不想让别人随便创建用户和修改自己的数据）。而”maindataabase"则是使用的数据库，默认为没有选择，需要用户自行选择。

    while True:
        user_e=input('PyDB>')
        User_database_path="PyDB/DataBase/"+admin

        这边的user_e就是用户输入的语句，“User_database_path”则是用户的数据库路径。

        #----------------------------------------------帮助列表
        if user_e=='@h' or user_e=='@help':
            DBhelp()

        这个帮助函数（DBhelp）是这样子的，要放在循环前，不然会报错：

def DBhelp():
    print("Command list:")
    print("|Command             |Explain                                         |")
    print("-----------------------------------------------------------------------")
    print("|@choose             |Choose a database to use.                       |")
    print("|@create table       |Generate a table under the current database.    |")

    if host["Jurisdiction"]=="Root":
        print("|@create user        |Create a new user.                              |")
    print("|@c or @continue     |Clear the current input statement.              |")
    print("|@create database    |Create a database according to the boot.        |")
    print("|@del table          |Delete a table.                                 |")
    print("|@del database       |Delete a database.                              |")
    print("|@exit               |Exit the program.                               |")
    print("|@h or @help         |Get the command list.                           |")
    print("|@insert             |Insert data into a table.                       |")
    print("|@show users         |View all users.                                 |")
    print("|@show tables        |View tables under the current database.         |")
    print("|@show database      |View the database under the current user.       |")
    print("|@query data         |Query data in the selected table.               |")
    print()

        就是一个命令列表，因为还在更新，所以不是很全。

        主要的命令列表是这样的：

Command（命令）

Explain（解释）

@choose

Choose a database to use.（选择一个需要使用的数据库）

@create table

Generate a table under the current database.（在当前数据库下创建一个表格）

@create user

Create a new user.（创建一个新用户）

@c or @continue

Clear the current input statement.（清除当前输入的语句）

@createdatabase

Create a database according to the boot.（根据引导创建数据库）

@del table

Delete a table.（删除一个表格）

@del database

Delete a database.（删除一个数据库）

@exit

Exit the program.（退出程序）

@h or @help

Get the command list.（获得指令列表）

@insert

Insert data into a table.（把数据插入到表格中）

@show users

View all users.（查看所有的用户）

@show tables

View tables under the current database.（查看当前数据库下的所有表格）

@show database

iew the database under the current user.（查看当前用户下的所有数据库）

@query data

Query data in the selected table.

        以上是这个数据库的指令列表（还在更新），所有的操作只需要根据引导去做即可。

        所有指令对应的操作都在后面（不是按表格顺序来）：

        清除当前输入的语句：

        if user_e=='@c' or user_e=='@continue':
            continue

        很简单，直接跳过就好了。

        退出程序：

        elif user_e=='@exit':
            print("PyDB>Thank you for your use~ :) Bye!")
            time.sleep(3)
            sys.exit()

        打印一个告别语，等待三秒，退出~~

        选择数据库：

        elif user_e=='@choose':
            maindatabase=input('Select>')
            find=os.listdir(User_database_path)
            yesorno=False
            for i in find:
                if i==maindatabase:
                    yesorno=True
            if yesorno==False:
                print("Error>This database does not exist.\n")
            else:
                print('PyDB>Database changed.\n')

        先获取输入的数据库，然后用os的lisetdir方法在当前用户文件夹下循环查找，如不存在则报错，若存在则说明“数据库改变了”，同时改变“maindatabae”。

        展示数据库：

        elif user_e=="@show database":
            database_num=os.listdir(User_database_path)
            databases=''
            if database_num==[]:
                print("PyDB>There is no database yet. Use '@create database' to create one!\n")
            else:
                for i in range(len(database_num)):
                    if i<len(database_num)-1:
                        databases+=database_num[i]+','
                    else:
                        databases+=database_num[i]
                print(" | "+databases+' |')

        用os库的listdir方法获取用户目录下的文件夹（数据库）并打印，若没有则提示创建一个。

        创建数据库：

        elif user_e=="@create database":

            database_num=os.listdir(User_database_path)
            basename=input("PyDB>Please enter the Name of the Database.\nCreate>")
            os.makedirs('./PyDB'+'./DataBase'+'./'+admin+'./'+basename)
            print("Success>Database creation succeeded!\n")

        同样用os的lisetdir方法判断该数据库是否存在，如不存在则创建并打印提示信息。

        创建表格：

        elif user_e=="@create table":
            if maindatabase=='':
                print("PyDB>Please choose a database first!\n")
            else:
                tablename=input('PyDB>Please enter the name of the table.\nCreate>')
                database_path=os.listdir('PyDB/Database/'+admin+'/'+maindatabase)
                yesorno=False
                for i in database_path:
                    i=i.replace(".json",'')
                    if i==tablename:
                        yesorno=True
                if yesorno==True:
                    print("Error>This table already exists.\n")
                else:
                    columns=input("PyDB>Please enter the title of each column.\nCreate>")
                    columns=columns.split(',')
                    column_dict={}
                    for i in range(len(columns)):
                        column_dict.setdefault(str(i+1),columns[i])
                    
                     
                   saveToJSON(column_dict,'Database/'+admin+'/'+maindatabase+'/'+tablename+'.json')
                   saveToJSON(',','Database/'+admin+'/'+maindatabase+'/'+tablename+'.json')
                   print("Success>Successfully created the table!\n")

          敲黑板了啊！这个是重点之一！首先，查看有没有选择数据库，然后就是老方法，用listdir判断是否存在这个表格。但是因为表格是用json文件格式储存的，所以在判断时必须在表格名称后面加上“.json”后缀或者将获取到的文件名称去掉后缀".json"，不然就无法正确的判断出是否存在这个表格。

        展示表格：

        elif user_e=="@show tables":
            if maindatabase=='':
                print("PyDB>Please choose a database first!\n")
            else:
                database_path=os.listdir('PyDB/Database/'+admin+'/'+maindatabase)
                if database_path==[]:
                    print("PyDB>There is no table yet. Use '@create table' to create one!\n")
                else:
                    show_tables=''
                    for i in range(len(database_path)):
                        toshow=database_path[i]
                        if i<len(database_path)-1:

                            show_tables+=toshow.replace('.json','')+','
                        else:
                            show_tables+=toshow.replace('.json','')
                    print(' |'+show_tables+' |\n')

        首先，查看有没有选择数据库，其他的和上面的展示数据库差不多，这里就不过多赘述了。

        删除数据库：

        elif user_e=="@del database":
            del_base=input("PyDB>Please enter the name of the database to delete.\nDelete>")
            database_path=os.listdir('PyDB/Database/'+admin)
            yesorno=False
            for i in database_path:
                if i==del_base:
                    yesorno=True
            if yesorno==False:
                print("Error>This database doesn't exists.\n")
            else:
                database_path=os.listdir('PyDB/Database/'+admin+'/'+del_base)
                if database_path==[]:
                    if maindatabase==del_base:
                        maindatabase=''
                    os.rmdir('PyDB/Database/'+admin+'/'+del_base)
                    print("Success> Successfully deleted this database!\n")
                else:
                    while True:
                        sure=input("\nPyDB>Are you sure to delete?This database is not empty!(Y/N)\nDelete>")
                        if sure=='Y' or sure=='y':
                            shutil.rmtree('PyDB/Database/'+admin+'/'+del_base)
                            print('Success> Successfully deleted this database!')
                            if maindatabase==del_base:
                                maindatabase=''
                            break
                        elif sure=='N' or sure=='n':
                            print('PyDB> Cancel deletion.\n')
                            break

        还是老方法，先用listdir判断这个数据库是否存在，如若存在，在判断这是不是个空数据库。如果是，那就是直接删掉；如果不是，则会提示这个数据库不为空，是否确定删除？确定了，那就用shutil的mrtree方法，循环删除数据库内的内容。

        今天的最后一个功能，也是数据库最核心的功能：插入数据

        elif user_e=="@insert":
            if maindatabase=='':
                print("PyDB>Please choose a database first!")
            else:
                insert_table=input("PyDB>Please choose a table.\nInsert>")
                find=os.listdir(User_database_path+'/'+maindatabase)
                yesorno=False
                for i in find:
                    if i==insert_table+'.json':
                        yesorno=True
                if yesorno==False:
                    print("Error>Sorry, this form does not exist.\n")
                else:
                    toshow=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')[0]
                    toshow=str(toshow).replace('{','')
                    toshow=toshow.replace('}','')
                    toshow=toshow.replace("'",'')
                    print("PyDB>The titles of the columns are |"+toshow+'|.')
                    toinsert=input("PyDB>Please enter the data to insert!\nInsert>")
                    toinsert=toinsert.split(',')
                    toshow=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')[0]
                    listshow=list(toshow)
                    tosave={}
                    if len(toinsert)==len(listshow):
                        for i in range(len(list(toshow))):
                            head=toshow[listshow[i]]
                            tosave.setdefault(head,toinsert[i])
                        waytos=input("PyDB>Please choose the way to insert!\nInsert>")
                        if waytos=='end':
                            try:
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif waytos=='top':
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    lastin.pop(0)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif len(turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json'))==int(waytos):
                            try:
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif int(waytos)==1:
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    lastin.pop(0)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif 1<int(waytos)<len(turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')):
                            inwaytos=int(waytos)
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    for i in range(inwaytos):
                                        lastin.pop(i)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                    else:
                        print('Error>The information entered is incorrect!\n')

        插入数据呢分为三种方式……详细呢，我们下节再介绍，嘿嘿嘿~~

        （其实python代码的可读性还是很高的，主要还是靠自己阅读代码，就和语文的阅读理解一样，多读才能提高水平~~好吧，说白了就是我懒QwQ）

        今日代码小结：

import json
import os
import sys
import time
import shutil
#-----------------------


def turn(file):
    with open(file,mode='r',encoding='utf-8') as f:
        a=f.readline()
        a=a.split('","')
        b=[]
        for i in range(len(a)):
            if i <= len(a)-2:
                b.append(json.loads(a[i]))
        return b
def saveToJSON(dicObject,file):
    flag=False
    '''if type(dicObject)!=dict:
        print('dict')
        return flag'''
    try:
        j_file=open("./PyDB/"+file,'a')
        json.dump(dicObject,j_file,ensure_ascii=False)
        flag=True
    except:
        print('写数据出错!')
    finally:
        if flag:
            j_file.close()
    return flag
#=========================
def GetFromJSON(filename):
    flag=False
    dicObject={}
    try:
        way="./PyDB/"+filename
        j_file=open(way,'r')
        dicObject=json.load(j_file)
        flag=True
    except:
        flag=False
    finally:
        if flag:
            j_file.close()
        elif flag==False:
            return False
    return dicObject

#----------------------------------------
def DBhelp():
    print("Command list:")
    print("|Command             |Explain                                         |")
    print("-----------------------------------------------------------------------")
    print("|@choose             |Choose a database to use.                       |")
    print("|@create table       |Generate a table under the current database.    |")

    if host["Jurisdiction"]=="Root" or host["Jurisdiction"]=="Hang Jiayu":
        print("|@create user        |Create a new user.                              |")
    print("|@c or @continue     |Clear the current input statement.              |")
    print("|@create database    |Create a database according to the boot.        |")
    print("|@del table          |Delete a table.                                 |")
    print("|@del database       |Delete a database.                              |")
    print("|@exit               |Exit the program.                               |")
    print("|@h or @help         |Get the command list.                           |")
    print("|@insert             |Insert data into a table.                       |")
    print("|@show users         |View all users.                                 |")
    print("|@show tables        |View tables under the current database.         |")
    print("|@show database      |View the database under the current user.       |")
    print("|@query data         |Query data in the selected table.               |")
    print()





#----------------------------------------
if __name__ == '__main__':
    print("| Welcome to PyDB Monitor.")
    print("| Server version: 1.0.0 PyDB Server.")
    print("| Add '@' at the beginning of the statement.")
    print("| Type '@help' or '@h' for help.Type '@continue' or '@c' to clear the current input statement.\n")
    print("PyDB>Welcome to PyDB!"+"\n")
    folder=''
    for i in range(len(os.listdir())):
        a=os.listdir()
        if a[i]=='PyDB':
            folder='PyDB'
    if folder!='PyDB':
        os.makedirs('./PyDB'+'./user')
        os.makedirs('./PyDB'+'./DataBase')
    #----------------------------------------------------Sing in
    while True:

        if len(os.listdir('./PyDB/user'))==0:
            print("PyDB> There are no users yet :( ...  Let's create one! :) \n")
            admin=input("PyDB>  Please enter your User Name!\nAdministrator>")
            Pass=input("PyDB> Please enter your password!\nPassword>")
            RePass=input("PyDB> Please enter your password again!\nPassword>")
            if Pass==RePass:
                info={
                    'Name':admin,'Password':Pass,'Jurisdiction':'Root'
                }
                saveToJSON(info,'user/'+admin+'.json')
                print("\nSuccess>Congratulations, account creation succeeded!\n")
                host=GetFromJSON("user/"+admin+".json")
                os.makedirs('./PyDB'+'./DataBase'+'./'+admin)
                break
            else:
                while True:
                    print('PyDB>The two passwords you entered are different. Please try again.')
                    Pass=input("PyDB> Please enter your password!\nPassword>")
                    RePass=input("PyDB> Please enter your password again!\nPassword>")
                    if Pass==RePass:
                        info={
                            'User':admin,'Password':Pass,'Jurisdiction':'Root'
                        }
                        saveToJSON(info,'user/'+admin+'.json')
                        print("\nSuccess>Congratulations, account creation succeeded!\n")
                        host=GetFromJSON("user/"+admin+".json")
                        os.makedirs('./PyDB'+'./DataBase'+'./'+admin)
                        break
                    break
        else:
            while True:
                admin=input('User name>')
                if admin=="@exit":
                    print("PyDB>Thank you for your use~ :) Bye!")
                    time.sleep(3)
                    sys.exit()
                if GetFromJSON("user/"+admin+".json")==False:
                    print("Error>Sorry, there is no such user.Please try again.")
                else:
                    host=GetFromJSON("user/"+admin+".json")
                    break
            Pass=input('Password>')
            if Pass=="@exit":
                print("PyDB>Thank you for your use~ :) Bye!")
                time.sleep(3)
                sys.exit()
            if host["Password"]!=Pass:
                print("Error>Password error, please try again!")
                Pass=input('Password>')
                host=GetFromJSON("user/"+admin+".json")
                if host["Password"]!=Pass:
                    print("Error>Password error, please try again!")
                    Pass=input('Password>')
                    host=GetFromJSON("user/"+admin+".json")
                    if host['Password']!=Pass:
                        print("Error>You have made three consecutive errors. Please try again later.")
                        time.sleep(3)
                        sys.exit()
                    else:
                        print("\n"+"PyDB>Welcome,"+admin+'!\n')
                        break
                else:
                    print("\n"+"PyDB>Welcome,"+admin+'!\n')
                    break
            else:
                print("\n"+"PyDB>Welcome,"+admin+'!\n')
                break



    jurisdiction=host["Jurisdiction"]
    maindatabase=''



    #-----------------------------------------------------------Console
    while True:
        user_e=input('PyDB>')
        User_database_path="PyDB/DataBase/"+admin

        #----------------------------------------------Help
        if user_e=='@h' or user_e=='@help':
            DBhelp()
        #----------------------------------------------continue
        if user_e=='@c' or user_e=='@continue':
            continue
        #----------------------------------------------Exit
        elif user_e=='@exit':
            print("PyDB>Thank you for your use~ :) Bye!")
            time.sleep(3)
            sys.exit()
        #----------------------------------------------Choose Database
        elif user_e=='@choose':
            maindatabase=input('Select>')
            find=os.listdir(User_database_path)
            yesorno=False
            for i in find:
                if i==maindatabase:
                    yesorno=True
            if yesorno==False:
                print("Error>This database does not exist.\n")
            else:
                print('PyDB>Database changed.\n')
        #----------------------------------------------Show Database
        elif user_e=="@show database":
            database_num=os.listdir(User_database_path)
            databases=''
            if database_num==[]:
                print("PyDB>There is no database yet. Use '@create database' to create one!\n")
            else:
                for i in range(len(database_num)):
                    if i<len(database_num)-1:
                        databases+=database_num[i]+','
                    else:
                        databases+=database_num[i]
                print(" | "+databases+' |')
        #----------------------------------------------Create Database
        elif user_e=="@create database":

            database_num=os.listdir(User_database_path)
            basename=input("PyDB>Please enter the Name of the Database.\nCreate>")
            os.makedirs('./PyDB'+'./DataBase'+'./'+admin+'./'+basename)
            print("Success>Database creation succeeded!\n")
        #----------------------------------------------Create Table
        elif user_e=="@create table":
            if maindatabase=='':
                print("PyDB>Please choose a database first!\n")
            else:
                tablename=input('PyDB>Please enter the name of the table.\nCreate>')
                database_path=os.listdir('PyDB/Database/'+admin+'/'+maindatabase)
                yesorno=False
                for i in database_path:
                    i=i.replace(".json",'')
                    if i==tablename:
                        yesorno=True
                if yesorno==True:
                    print("Error>This table already exists.\n")
                else:
                    columns=input("PyDB>Please enter the title of each column.\nCreate>")
                    columns=columns.split(',')
                    column_dict={}
                    for i in range(len(columns)):
                        column_dict.setdefault(str(i+1),columns[i])
                    print("Success>Successfully created the table!\n")
                    saveToJSON(column_dict,'Database/'+admin+'/'+maindatabase+'/'+tablename+'.json')
                    saveToJSON(',','Database/'+admin+'/'+maindatabase+'/'+tablename+'.json')
        #----------------------------------------------show tables
        elif user_e=="@show tables":
            if maindatabase=='':
                print("PyDB>Please choose a database first!\n")
            else:
                database_path=os.listdir('PyDB/Database/'+admin+'/'+maindatabase)
                if database_path==[]:
                    print("PyDB>There is no table yet. Use '@create table' to create one!\n")
                else:
                    show_tables=''
                    for i in range(len(database_path)):
                        toshow=database_path[i]
                        if i<len(database_path)-1:

                            show_tables+=toshow.replace('.json','')+','
                        else:
                            show_tables+=toshow.replace('.json','')
                    print(' |'+show_tables+' |\n')
        #----------------------------------------------delete database
        elif user_e=="@del database":
            del_base=input("PyDB>Please enter the name of the database to delete.\nDelete>")
            database_path=os.listdir('PyDB/Database/'+admin)
            yesorno=False
            for i in database_path:
                if i==del_base:
                    yesorno=True
            if yesorno==False:
                print("Error>This database doesn't exists.\n")
            else:
                database_path=os.listdir('PyDB/Database/'+admin+'/'+del_base)
                if database_path==[]:
                    if maindatabase==del_base:
                        maindatabase=''
                    os.rmdir('PyDB/Database/'+admin+'/'+del_base)
                    print("Success> Successfully deleted this database!\n")
                else:
                    while True:
                        sure=input("\nPyDB>Are you sure to delete?This database is not empty!(Y/N)\nDelete>")
                        if sure=='Y' or sure=='y':
                            shutil.rmtree('PyDB/Database/'+admin+'/'+del_base)
                            print('Success> Successfully deleted this database!')
                            if maindatabase==del_base:
                                maindatabase=''
                            break
                        elif sure=='N' or sure=='n':
                            print('PyDB> Cancel deletion.\n')
                            break
        #----------------------------------------------insert data
        elif user_e=="@insert":
            if maindatabase=='':
                print("PyDB>Please choose a database first!")
            else:
                insert_table=input("PyDB>Please choose a table.\nInsert>")
                find=os.listdir(User_database_path+'/'+maindatabase)
                yesorno=False
                for i in find:
                    if i==insert_table+'.json':
                        yesorno=True
                if yesorno==False:
                    print("Error>Sorry, this form does not exist.\n")
                else:
                    toshow=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')[0]
                    toshow=str(toshow).replace('{','')
                    toshow=toshow.replace('}','')
                    toshow=toshow.replace("'",'')
                    print("PyDB>The titles of the columns are |"+toshow+'|.')
                    toinsert=input("PyDB>Please enter the data to insert!\nInsert>")
                    toinsert=toinsert.split(',')
                    toshow=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')[0]
                    listshow=list(toshow)
                    tosave={}
                    if len(toinsert)==len(listshow):
                        for i in range(len(list(toshow))):
                            head=toshow[listshow[i]]
                            tosave.setdefault(head,toinsert[i])
                        waytos=input("PyDB>Please choose the way to insert!\nInsert>")
                        if waytos=='end':
                            try:
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif waytos=='top':
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    lastin.pop(0)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif len(turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json'))==int(waytos):
                            try:
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif int(waytos)==1:
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    lastin.pop(0)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                        elif 1<int(waytos)<len(turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')):
                            inwaytos=int(waytos)
                            try:
                                lastin=turn(User_database_path+'/'+maindatabase+'/'+insert_table+'.json')
                                with open(User_database_path+'/'+maindatabase+'/'+insert_table+'.json',mode='w',encoding='utf-8') as f:
                                    json.dump(lastin[0],f)
                                    for i in range(inwaytos):
                                        lastin.pop(i)
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(tosave,'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                for i in range(len(lastin)):
                                    saveToJSON(lastin[i],'DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                    saveToJSON(',','DataBase/'+admin+'/'+maindatabase+'/'+insert_table+'.json')
                                print("Success>Successfully inserted data!\n")
                            except:
                                print("Error>There is some thing wrong with saving it!\n")
                    else:
                        print('Error>The information entered is incorrect!\n')

        那么今天的介绍就到这里了，如果大家有建议或更好的方法，欢迎在评论区留言哦！我们下期再见，Bye~~

        （PS：其中一段代码有个小细节哦~找到的人在评论区打出来吧~）