如何在特定行添加字符串

Question

我有一个文件，里面有50行内容。我想用Python或者Linux的方法，在第20行加上一个字符串“-----”。

Answer 1

如果要读取的文件很大，而你又不想一次性把整个文件都加载到内存中：

from tempfile import mkstemp
from shutil import move
from os import remove, close

line_number = 20

file_path = "myfile.txt"

fh_r = open(file_path)
fh, abs_path = mkstemp()
fh_w = open(abs_path, 'w')

for i, line in enumerate(fh_r):
    if i == line_number - 1:
        fh_w.write('-----' + line)
    else:
        fh_w.write(line)

fh_r.close()
close(fh)
fh_w.close()

remove(file_path)
move(abs_path, file_path)

注意：我参考了Alok的回答，详细内容可以在这里找到。

Answer 2

$ head -n 20 input.txt > output.txt
$ echo "---" >> output.txt
$ tail -n 30 input.txt >> output.txt

当然可以！请把你想要翻译的内容发给我，我会帮你把它变得简单易懂。

Answer 3

你试过这样做吗？：

exp = 20 # the line where text need to be added or exp that calculates it for ex %2

with open(filename, 'r') as f:
    lines = f.readlines()

with open(filename, 'w') as f:
    for i,line in enumerate(lines):
        if i == exp:
            f.write('------')
        f.write(line)

如果你需要编辑不同数量的行，可以按照上面的方式更新代码：

def update_file(filename, ln):
    with open(filename, 'r') as f:
        lines = f.readlines()

    with open(filename, 'w') as f:
        for idx,line in enumerate(lines):
            (idx in ln and f.write('------'))
            f.write(line)