在python中匹配之前添加文本2行

Question

I am trying to find "AAXX" and add the word "Hello" two lines above:

Input:
111
222
AAXX
333
444
AAXX
555
666
AAXX

Output: 
Hello 
111
222
AAXX
Hello
333 
444
AAXX
Hello
555
666
AAXX

I have managed to insert only one "Hello" two lines before the first "AAXX" by using the code below, but I cannot make it loop through the file and do the same for all "AAXX" matches.

import os

with open(os.path.expanduser("~/Desktop/test.txt"), "r+") as f:
    a = [x.rstrip() for x in f]
    for i, item in enumerate(a):
        if item.startswith("AAXX"):
            a.insert(i-2,"Hello")
            break
        index += 1
    # Go to start of file and clear it
    f.seek(0)
    f.truncate()
    # Write each line back
    for line in a:
        f.write(line + "\n")

So far, I get:

Hello
111
222
AAXX
333
444
AAXX
555
666
AAXX

Answer 1

def p(a):
    r = []
    for i, item in enumerate(a):
        if item.startswith("AAXX"):
            r.append(i)
    for i in reversed(r):
        a.insert(i-2,"HELLO")
    return(a)

You may wrap this up as you wish to deal with inputs/outputs. You need to fix up the case where "AAXX" occurs within the first two items, as you haven't defined what behaviour you want there. The key issue is that modifying the list as you iterate over it is bad practice, in particular the later indices can be off because you've inserted earlier "HELLO"s. A possible solution is to keep track of all the insertion indices, then do the insertions in reverse order, because inserting later in the list doesn't affect the earlier indices.

Answer 2

Can you try the following:

with open('test.txt', 'r') as infile:
    data = infile.read()
final_list = []
for ind, val in enumerate(data.split('\n')):
    final_list.append(val)
    if val == 'AAXX':
        final_list.insert(-3, 'HELLO')
# save the text file
with open('test.txt', 'w') as outfile:
    data = outfile.write('\n'.join(final_list))

Output:

HELLO
111
222
AAXX
HELLO
333
444
AAXX
HELLO
555
666
AAXX