文章目录

问题描述

1.读进列表后覆盖原文件

2.FileInput类

3.seek

对比

遇到的坑

参考文献

问题描述

Python匹配文本并在其上一行追加文本

test.txt

a

b

c

d

e

1.读进列表后覆盖原文件

def match_then_insert(filename, match, content):

    """匹配后在该行追加 :param filename: 要操作的文件 :param match: 匹配内容 :param content: 追加内容 """

    lines = open(filename).read().splitlines()

    index = lines.index(match)

    lines.insert(index, content)

    open(filename, mode='w').write('\n'.join(lines))





match_then_insert('test.txt', match='c', content='123')

效果

a

b

123

c

d

e

2.FileInput类

from fileinput import FileInput





def match_then_insert(filename, match, content):

    """匹配后在该行追加 :param filename: 要操作的文件 :param match: 匹配内容 :param content: 追加内容 """

    for line in FileInput(filename, inplace=True):  # 原地过滤

        if match in line:

            line = content + '\n' + line

        print(line, end='')  # 输出重定向到原文件





match_then_insert('test.txt', match='c', content='123')

3.seek

def match_then_insert(filename, match, content):

"""匹配后在该行追加 :param filename: 要操作的文件 :param match: 匹配内容 :param content: 追加内容 """

with open(filename, mode='rb+') as f:

while True:

try:

line = f.readline()  # 逐行读取

except IndexError:  # 超出范围则退出

break

line_str = line.decode().splitlines()[0]

if line_str == match:

f.seek(-len(line), 1)  # 光标移动到上一行

rest = f.read()  # 读取余下内容

f.seek(-len(rest), 1)  # 光标移动回原位置

f.truncate()  # 删除余下内容

content = content + '\n'

f.write(content.encode())  # 插入指定内容

f.write(rest)  # 还原余下内容

break

match_then_insert('test.txt', match='c', content='123')

对比

from timeit import timeit

from fileinput import FileInput

def init_txt():

open('test.txt', mode='w').write('\n'.join(['a', 'b', 'c', 'd', 'e']))

def f1(filename='test.txt', match='c', content='123'):

lines = open(filename).read().splitlines()

index = lines.index(match)

lines.insert(index, content)

open(filename, mode='w').write('\n'.join(lines))

def f2(filename='test.txt', match='c', content='123'):

for line in FileInput(filename, inplace=True):

if match in line:

line = content + '\n' + line

print(line, end='')

def f3(filename='test.txt', match='c', content='123'):

with open(filename, mode='rb+') as f:

while True:

try:

line = f.readline()

except IndexError:

break

line_str = line.decode().splitlines()[0]

if line_str == match:

f.seek(-len(line), 1)

rest = f.read()

f.seek(-len(rest), 1)

f.truncate()

content = content + '\n'

f.write(content.encode())

f.write(rest)

break

init_txt()

print(timeit(f1, number=1000))

init_txt()

print(timeit(f2, number=1000))

init_txt()

print(timeit(f3, number=1000))

遇到的坑

报错可试试在文件头部添加

# -*- coding: utf-8 -*-

或指定 encoding='utf-8'

参考文献

open — Python 文档

Python3 open() 函数 | 菜鸟教程

open文件操作之mode模式剖析

Python文件打开方式详解——a、a+、r+、w+、rb、rt

python 文件混合读写模式 mode=‘r+’

python下在txt指定行追加文本

如何流式读取数G超大文件

Python3 seek()中间追加失败