writing specific lines from one file to another file

Question

I'm trying to read a file, look for a specific word and if a line contains that word, remove the line and send the remaining lines to a new file. Here's what I have but it is only finding one of the lines not all of them;

with open('letter.txt') as l:
  for lines in l:
    if not lines.startswith("WOOF"):
      with open('fixed.txt', 'w')as f:
        print(lines.strip(), file=f)

Answer 1

The problem is that when you do with open('fixed.txt', 'w') as f: you basically overwrite the entire content of the file with that one next line. Either open the file in append mode a ...

with open('letter.txt') as l:
    for lines in l:
        if not lines.startswith("WOOF"):
            with open('fixed.txt', 'a') as f:
                print(lines.strip(), file=f)

... or (probably better) open the file in w mode, but just once at the beginning:

with open('letter.txt') as l, open('fixed.txt', 'w') as f:
    for lines in l:
        if not lines.startswith("WOOF"):
            print(lines.strip(), file=f)