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()