def write_file():

""" 文件写入"""

file_name = "wri2te_test.txt"

# 以写入的方式打开

f = open(file_name,'w')

# 写入内容

f.write('hello')

# 换行符

f.write('\n')

# 写入内容

f.write('world')

# 关闭文件

f.close()

def write_mult_line():

""" 多行写入"""

file_name = 'write_mult_line.txt'

with open(file_name, 'w', encoding = 'utf-8') as f:

# \r\n 换两行

# \n 换一行

l = ['第1行','\n','第2行','\r\n','第3行','\n','第4行']

f.writelines(l)

import random

from datetime import datetime

def write_user_log():

""" 记录用户日志"""

rest = "用户: {0} - 访问时间 {1}".format(random.randint(1000,9999), datetime.now())

print (rest)

file_name = 'write_user_log.txt'

# 追加

with open(file_name, 'a', encoding = 'utf-8') as f:

f.write(rest + '\n')

def read_and_write():

""" 先读，再写入"""

file_name = 'read_and_write.txt'

with open(file_name, 'r+', encoding="utf-8") as f:

read_rest = f.read()

# 判断如果没有1 写一行 aaa

# 判断如果有1 写一行 bbb

if '1' in read_rest:

f.write('\n')

f.write('aaa')

else:

f.write('bbb')

if __name__ == '__main__':

# write_file()

# write_mult_line()

# write_user_log()

read_and_write()