在文本文件中删除和插入行

Question

我有一个文本文件，内容如下：

first line  
second line  
third line  
forth line  
fifth line  
sixth line

我想把第三和第四行替换成三行新的内容。这样，上面的内容就会变成：

first line  
second line  
new line1  
new line2  
new line3    
fifth line  
sixth line

我该如何用Python来实现这个呢？

Answer 1

把整个文件读成一行一行的列表，然后用你想删除的行替换成一个新的行列表：

f = open('file.txt')
data = f.readlines()
f.close()
data[2:4] = [
    'new line1\n',
    'new line2\n',
    'new line3\n']
f = open('processed.txt','w')
f.writelines(data)
f.close()

注意，列表的切片是从零开始的，[2:4]的意思是“从第2个元素开始，到第4个元素之前的所有元素”。

Answer 2

import fileinput
myinsert="""new line1\nnew line2\nnew line3"""
for line in fileinput.input("file",inplace=1):
    linenum=fileinput.lineno()
    if linenum==1 or linenum>4 : 
        line=line.rstrip()
    if linenum==2:
        line=line+myinsert
    print line

import os
myinsert=["new line3\n","new line2\n","new line1\n"]
data=open("file").readlines()
data[2:4]=""
for i in myinsert:data.insert(2,i)
open("outfile","w").write(''.join(data))
os.rename("outfile","file)

或者如果你的文件不太大，

Answer 3

对于python2.6

with open("file1") as infile:
    with open("file2","w") as outfile:
        for i,line in enumerate(infile):
            if i==2:
                # 3rd line
                outfile.write("new line1\n")
                outfile.write("new line2\n")
                outfile.write("new line3\n")
            elif i==3:
                # 4th line
                pass
            else:
                outfile.write(line)

对于python3.1

with open("file1") as infile, open("file2","w") as outfile:
    for i,line in enumerate(infile):
        if i==2:
            # 3rd line
            outfile.write("new line1\n")
            outfile.write("new line2\n")
            outfile.write("new line3\n")
        elif i==3:
            # 4th line
            pass
        else:
            outfile.write(line)