基础操作

1. 打开file = open('1.txt',访问方式,encoding='编码方式')
2. 读text = file.read()
3. 关闭file.close()

访问方式

r:只读
w:只写，如果存在会覆盖，文件不存在创建新文件
a:追加，如果存在指针会放在文件结尾，不存在创建
r+:读写，指针在开头，不存在刨出异常
w+:读写，存在会覆盖，不存在创建
a+读写，指针在结尾，不存在创建

按行读取

text = file.readline().strip()#strip去除结尾换行

for i in file.readlines():
    # readlines返回一个可迭代对象并且每个元素都是一行

with结构

with open('xxx.txt') as file1:
    text = file1.read()

案例

修改文件

import os with open('a.txt') as read_f,open('a.txt.new','w') as write_f:
 data = read_f.read() 
 data = data.replace('Hello','nihao') 
 write_f.write(data) 
 
os.remove('a.txt') 
os.rename('a.txt.new','a.txt')

计算总价

文件a.txt内容：每一行内容分别为商品名字，价钱，个数。
apple 10 3
tesla 100000 1
mac 3000 2
lenovo 30000 3
chicken 10 3
通过代码，将其构建成这种数据类型：[{'name':'apple','price':10,'amount':3},
{'name':'tesla','price':1000000,'amount':1}......] 并计算出总价钱。

file = open('1.txt','r',encoding='utf-8')
line = []
list = []
for i in file.readlines():
     line = i.strip().split(' ')
     print(line)
     dict = {'name':line[0],'price':line[1],'count':line[2]}
     list.append(dict)

print(list)
sum = 0
for i in list:
    sum = sum + float(i['price'])*float(i['count'])

print(sum)

file.close()

模拟用户注册登陆

用户的信息需要保存在文件db.txt中
菜单:
供用户 选择时注册还是登陆
注册:
由用户输入用户名和密码
密码必须由字母和数字组成，长度不得小于8位
密码需要输入两次，并且判断密码是否相等，如果不相等注册失败
注册成功的话需要将用户信息写入db.txt中.
登陆:
由用户输入用户名和密码
用户名不存在时返回“用户不存在"
用户名存在密码错误时返回“密码错误”
密码重试超过三次，15秒之内不允许登陆
登陆成功时返回“欢迎登陆成功!”

import re
def SingUp():#注册
    file = open('db.txt','a')
    username = input('please input your username')
    while True:
        password = input('please input your password')
        passwor2 = input('please input your password once again')
        if re.match("^(?:(?=.*[A-Za-z])(?=.*[0-9])).*$",password):
            if len(password) >=8:
                if password == passwor2:
                    file.write(f'{username} {password} \n')
                    print(f'welcom {username}')
                    break
                else:
                    print('the two password are different!please input again!')
            else:
                print('your password is too short!')
        else:
            print('password must have number and words!')


    file.close()

def SignIn():#登录
    list = []
    k = 0
    flag = 0
    flag1 = 0
    file = open('db.txt','r')
    cont = file.readlines()
    for i in cont:
        tmp = i.strip().split(' ')
        person = {'username':tmp[0],'password':tmp[1]}
        list.append(person)
        k += 1
    username = input('please input your username')
    for i in list:
        if username == i['username']:
            flag = 1
            flag1 = list.index(i)
            break
            # password = input('please input your password')
            # if password == i['password']:
            #     print(f'hello {username}!')
            # else:
            #     print('wrong password!')
            #     flag += 1
            # if flag > 3:
            #     break

        else:
            print('user do not exist!')
            break
    if flag == 1:
        for i in range(3):
            password = input('please input your password')
            if list[flag1]['password'] == password:
                print(f'hello {username}!')
                break
            else:
                print('wrong password!')
    file.close()


def Menu():#菜单
    print('''
-------------Welcome-------------
Please input a number to choose :
--1. signup--
--2. signin--
---------------------------------
    ''')

if __name__ == '__main__':
    while True:
        Menu()
        num = input()
        if num == '1':
            SingUp()
        if num == '2':
            SignIn()
        else:
            print('please input a right number!')

加时间戳版本

import re
import time
def SingUp():#注册
    file = open('db.txt','a')
    username = input('please input your username')
    while True:
        password = input('please input your password')
        passwor2 = input('please input your password once again')
        if re.match("^(?:(?=.*[A-Za-z])(?=.*[0-9])).*$",password):
            if len(password) >=8:
                if password == passwor2:
                    file.write(f'{username} {password} 0\n')
                    print(f'welcom {username}')
                    break
                else:
                    print('the two password are different!please input again!')
            else:
                print('your password is too short!')
        else:
            print('password must have number and words!')


    file.close()

def SignIn():#登录
    list = []
    k = 0
    flag = 0
    flag1 = 0
    times = 0
    now = time.time()
    file = open('db.txt','r')
    cont = file.readlines()
    for i in cont:
        tmp = i.strip().split(' ')
        person = {'username':tmp[0],'password':tmp[1],'timemark':float(tmp[2])}
        list.append(person)
        k += 1
    # print(list)
    username = input('please input your username')
    for i in list:
        if username == i['username']:
            if ((now - i['timemark']) > 15):
                flag = 1
                flag1 = list.index(i)
                break
            else:print('wait! 15s !',now)
        else:
            if list.index(i) == len(list) - 1:
                print('user do not exist!')
                break
    if flag == 1:
        for i in range(3):
            password = input('please input your password')
            if list[flag1]['password'] == password:
                print(f'hello {username}!')
                break
            else:
                times += 1
                print('wrong password!')
                if times >= 3:
                    tt = list[flag1]['password']
                    cont[flag1] = f'{username} {tt} {time.time()}\n'
                    # print(cont)
                    with open('db.txt','w') as f:
                        for i in cont:
                            f.write(i)
    file.close()


def Menu():#菜单
    print('''
-------------Welcome-------------
Please input a number to choose :
--1. signup--
--2. signin--
---------------------------------
    ''')

if __name__ == '__main__':
    while True:
        Menu()
        num = input()
        if num == '1':
            SingUp()
        if num == '2':
            SignIn()
        else:
            print('please input a right number!')