python修改文件时，使用w模式会将原本的文件清空/覆盖。可以先用读（r）的方式打开，写到内存中,然后再用写（w）的方式打开。
1、替换文本中的taste 为 tasting
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Yesterday when I was young
昨日当我年少轻狂
The taste of life was sweet
生命的滋味是甜的
As rain upon my tongue
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#将文件读取到内存中
with open("./fileread.txt","r",encoding="utf-8") as f:
lines = f.readlines()
#写的方式打开文件
with open("./fileread.txt","w",encoding="utf-8") as f_w:
for line in lines:
if "taste" in line:
#替换
line = line.replace("taste","tasting")
f_w.write(line)
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2、全文中搜索替换或者单行替换
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#文本内容
Yesterday when I was young
昨日当我年少轻狂
The taste of life was sweet
生命的滋味是甜的
As rain upon my tongue
taste
taste
taste
taste
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#定义一个函数，带有4个参数
#x 表示要更新的文件名称
#y 表示要被替换的内容
#z 表示 替换后的内容
#s 默认参数为 1 表示只替换第一个匹配到的字符串
# 如果参数为 s = 'g' 则表示全文替换
def string_switch(x,y,z,s=1):
with open(x, "r", encoding="utf-8") as f:
#readlines以列表的形式将文件读出
lines = f.readlines()
with open(x, "w", encoding="utf-8") as f_w:
#定义一个数字，用来记录在读取文件时在列表中的位置
n = 0
#默认选项，只替换第一次匹配到的行中的字符串
if s == 1:
for line in lines:
if y in line:
line = line.replace(y,z)
f_w.write(line)
n += 1
break
f_w.write(line)
n += 1
#将剩余的文本内容继续输出
for i in range(n,len(lines)):
f_w.write(lines[i])
#全局匹配替换
elif s == 'g':
for line in lines:
if y in line:
line = line.replace(y,z)
f_w.write(line)
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测试
1)默认参数 1，只替换匹配到的第一行
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string_switch("fileread.txt","taste","tasting")
#结果
Yesterday when I was young
昨日当我年少轻狂
The tasting of life was sweet
生命的滋味是甜的
As rain upon my tongue
taste
taste
taste
taste
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2)全局替换
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string_switch("fileread.txt","taste","tasting","g")
#结果
Yesterday when I was young
昨日当我年少轻狂
The tasting of life was sweet
生命的滋味是甜的
As rain upon my tongue
tasting
tasting
tasting
tasting
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以上这篇python基础_文件操作实现全文或单行替换的方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：http://www.cnblogs.com/bigberg/p/6489043.html