在特定行之后添加行

Question

我正在尝试将特定行添加到文件中的特定区域。 我正在使用这个：

new_file = open("file.txt", "r+")
 for line in new_file:
  if line == "; Include below":
     line = line + "\nIncluded text"
     new_file.write(line)
  else:
     new_file.write(line)

但由于某种原因，我的file.txt 的内容重复了。

编辑：如果我的文件看起来像：

blablablablablablabal
balablablabalablablbla
include below
blablablablablabalablab
ablablablabalbalablaba

我想让它看起来像：

blablablablablablabal
balablablabalablablbla
include below
included text
blablablablablabalablab
ablablablabalbalablaba

Answer 1

读取时不能安全地写入文件，最好将文件读入内存，更新并重写到文件。

with open("file.txt", "r") as in_file:
    buf = in_file.readlines()

with open("file.txt", "w") as out_file:
    for line in buf:
        if line == "; Include this text\n":
            line = line + "Include below\n"
        out_file.write(line)

Answer 2

这就是我所做的。

def find_append_to_file(filename, find, insert):
    """Find and append text in a file."""
    with open(filename, 'r+') as file:
        lines = file.read()

        index = repr(lines).find(find) - 1
        if index < 0:
            raise ValueError("The text was not found in the file!")

        len_found = len(find) - 1
        old_lines = lines[index + len_found:]

        file.seek(index)
        file.write(insert)
        file.write(old_lines)
# end find_append_to_file

Answer 3

使用sed:

$ sed '/^include below/aincluded text' < file.txt

解释：

• /^include below/：匹配以 include below 开头的每一行 (^)
• a：添加换行符和以下文本
• includeed text：a 附加的文字

编辑：使用 Python：

for line in open("file.txt").readlines():
    print(line, end="")
    if line.startswith("include below"):
        print("included text")