Remove lines that contain certain string

You can make your code simpler and more readable like this

bad_words = ['bad', 'naughty']with open('oldfile.txt') as oldfile, open('newfile.txt', 'w') as newfile:    for line in oldfile:        if not any(bad_word in line for bad_word in bad_words):            newfile.write(line)

using a Context Manager and any.

I have used this to remove unwanted words from text files:

bad_words = ['abc', 'def', 'ghi', 'jkl']with open('List of words.txt') as badfile, open('Clean list of words.txt', 'w') as cleanfile:    for line in badfile:        clean = True        for word in bad_words:            if word in line:                clean = False        if clean == True:            cleanfile.write(line)

Or to do the same for all files in a directory:

import osbad_words = ['abc', 'def', 'ghi', 'jkl']for root, dirs, files in os.walk(".", topdown = True):    for file in files:        if '.txt' in file:            with open(file) as filename, open('clean '+file, 'w') as cleanfile:                for line in filename:                    clean = True                    for word in bad_words:                        if word in line:                            clean = False                    if clean == True:                        cleanfile.write(line)

I'm sure there must be a more elegant way to do it, but this did what I wanted it to.

You could simply not include the line into the new file instead of doing replace.

for line in infile :     if 'bad' not in line and 'naughty' not in line:            newopen.write(line)