Python3实现文件的增删改查操作

#_*_coding:utf-8_*_
import os
#文件处理
def file_handle(filename,backend_data,record_list=None,type='fetch'):
    new_file=filename+'_new'    #新的文件名字
    bak_file=filename+'_bak'    #把新的文件名改成bak
    if type == 'fetch':
        r_list = []
        with open(filename, 'r') as f:
            tag = False #定义一个tag很关键
            for line in f:
                if line.strip() == backend_data: #所查询的内容存在
                    tag = True
                    continue
                #读取到下一个backend结束
                if tag and line.startswith('backend'):
                    break
                if tag and line:
                    r_list.append(line.strip())
            for line in r_list:
                print(line)
            return r_list
    elif type == 'append': #添加的文件处理
        with open(filename, 'r') as read_file, \
                open(new_file, 'w') as write_file:
            for r_line in read_file: #把原文件的内容一一写到新的文件中
                write_file.write(r_line)

            for new_line in record_list:    #把添加的记录写到文件中
                if new_line.startswith('backend'):  #如果列表中的元素是以backend开头的，直接写

                    write_file.write(new_line + '\n')
                else:
                    write_file.write("%s%s\n" % (' ' * 8, new_line))    #否则先写8个空格，再写列表元素
        os.rename(filename, bak_file)
        os.rename(new_file, filename)
        os.remove(bak_file)#新文件覆盖原文件
    elif type == 'change':
        with open(filename, 'r') as read_file, \
                open(new_file, 'w') as write_file:
            tag=False
            has_write=False
            for r_line in read_file:
                if r_line.strip() == backend_data:
                    tag=True
                    continue
                if tag and r_line.startswith('backend'):
                    tag=False
                if not tag:
                    write_file.write(r_line)
                else:
                    if not has_write:
                        for new_line in record_list:
                            if new_line.startswith('backend'):
                                write_file.write(new_line+'\n')
                            else:
                                write_file.write('%s%s\n' %(' '*8,new_line))
                        has_write=True #很关键，否则会重复打印
        os.rename(filename, bak_file)
        os.rename(new_file, filename)
        os.remove(bak_file)