How can I delete lines consecutively in python text files?

Question

I'm trying to create a password generator that can delete lines consecutively off the password saver file. I've tried doing the same thing 4 times, but that doesn't work when trying to delete 4 lines after the 1st. Instead it deletes all the lines including that phrase of words. Here is some of my code:

with open("Password Saver.txt", "r+", encoding='utf-8') as file:
for line in file:
    if line.find(reason) != -1:
        for _ in range(4):
            next(file)
    else:
        Things2Keep = Things2Keep + (line.rstrip())
f = open("Password Saver.txt", "w")
f.write(Things2Keep)

Answer 1

Try the following:

file.write("This is a placeholder.\n")
reason = "google"
with open("Password Saver.rtf",'rb') as IN:
    lines = IN.readlines()

with open("Password Saver.rtf",'wb') as OUT:
    for line in lines:
         if line.lower().find(reason.lower()) != -1:
             OUT.write(line)

Also, I think .rtf files better be opened as binary.

Answer 2

So what I deduced from question and comments: remove the line that matches and four lines right after that.

Input

header
google
1
2
3
4
footer

Output

header
footer

Code

Normally I would introduce a counter to be incremented on every line after the match, but for this answer I prefer to go a bit crazy and skip lines as file-like object is an iterator:

with open(fname, 'r', encoding='utf-8') as file:
    for line in file:
        if line.find(reason) != -1:
            for _ in range(4):
                next(file)
        else:
            print(line.rstrip())

This is only to demonstrate the principle, adapt it for file manipulation yourself, as an exercise =)