human
Complete the below
def filter_file(regex, repl, *filenames, **kwargs):

    ''''Like sed, but uses python regular expressions.
    Filters every line of each file through regex and replaces the file
    with a filtered version.  Preserves mode of filtered files.
    As with re.sub, ``repl`` can be either a string or a callable.
    If it is a callable, it is passed the match object and should
    return a suitable replacement string.  If it is a string, it
    can contain ``\1``, ``\2``, etc. to represent back-substitution
    as sed would allow.
    Parameters:
    regex (str): The regular expression to search for
    repl (str): The string to replace matches with
    *filenames: One or more files to search and replace
    Keyword Arguments:
    string (bool): Treat regex as a plain string. Default it False
    backup (bool): Make backup file(s) suffixed with ``~``. Default is True
    ignore_absent (bool): Ignore any files that don\'t exist.
    Default is False'
    '''
assistant
#Here is the Python code you requested.
    string = kwargs.get('string', False)
    backup = kwargs.get('backup', True)
    ignore_absent = kwargs.get('ignore_absent', False)
    if (not callable(repl)):
        unescaped = repl.replace('\\\\', '\\')
        def replace_groups_with_groupid(m):
            def groupid_to_group(x):
                return m.group(int(x.group(1)))
            return re.sub('\\\\([1-9])', groupid_to_group, unescaped)
        repl = replace_groups_with_groupid
    if string:
        regex = re.escape(regex)
    for filename in filenames:
        backup_filename = (filename + '~')
        if (ignore_absent and (not os.path.exists(filename))):
            continue
        if (not os.path.exists(backup_filename)):
            shutil.copy(filename, backup_filename)
        try:
            for line in fileinput.input(filename, inplace=True):
                print re.sub(regex, repl, line.rstrip('\n'))
        except:
            shutil.move(backup_filename, filename)
            raise
        finally:
            if (not backup):
                os.remove(backup_filename)