How to remove line from the file in python [duplicate]

When you want to edit a file, you make a new file with the correct data and then rename the new file as the old file. This is what serious programs like your text editor probably do. (Some text editors actually do even weirder stuff, but there's no use going into that.) This is because in many filesystems the rename can be atomic, so that under no circumstances will you end up with the original file being corrupted.

This would lead to code to the effect of

with open(orig_file) as f, open(working_file, "w") as working: 
    # ^^^ 2.7+ form, 2.5+ use contextlib.nested
    for line in f:
        if '2' not in line: # Is this exactly the criterion you want?
                            # What if a line was "12 5"?
            working.write(line)

os.rename(working_file, orig_file)

You may want to use orig_file + '~' or the tempfile module for generating the working file.

with open('f', 'r+') as f:
  data = ''.join(filter(lambda l: '2' not in l.strip().split(' '), f))
  f.seek(0)
  f.truncate(0)
  f.write(data)

import fileinput
for line in fileinput.input('f',inplace =1):
  line = line.strip()
  if not '2' in line:
    print line