def __init__(self, pattern, replacement, is_multiline):
        """
        Initialize the Substitution:
            pattern: the pattern to match as will be passed to 're.sub'.
            replacement: the argument that will be passed as the replacement to
                're.sub'. This way it can employ r'\1' style matching of
                parenthesis captures.
            is_multiline: if True, the pattern will be compiled with the
                re.MULTILINE flag.
        """
        self.pattern = pattern
        self.repl = replacement
        self.is_multiline = is_multiline

        Initialize the Substitution:
            pattern: the pattern to match as will be passed to 're.sub'.
            replacement: the argument that will be passed as the replacement to
                're.sub'. This way it can employ r'' style matching of
                parenthesis captures.
            is_multiline: if True, the pattern will be compiled with the
                re.MULTILINE flag.
        
eg/substitute.py