PERL-style RegExp substitution in Python (but within "s/.../.../", uses Python syntax)

replace.py

#!/usr/bin/env python

# Python support for PERL's shorthand of pattern substitution (s/.../.../)
# Supports flags:
# i => case insensitive
# m => multiline match (caret and dollar represent line terminations, not whole-string)
# s => "dot-all" - dot matches everything, including new-line
# g => "global" - replace every instance (without this, only the first)

import re

sample = "#replace s@ABC(\@2)@\\1DEF@g"

RE_REPLACE_DIRECTIVE = '^#replace\s+(.*)$'

class ReplaceParser(object):
	RE_REPLACE_CORE = r'^s([@#%/])((?:\\\1|(?!\1).)*)\1((?:\\\1|(?!\1).)*)\1(\w*)$'

	FLAG_REF = {
		'i': re.IGNORECASE,
		'm': re.MULTILINE,
		's': re.DOTALL
	}

	def __init__(self, replacement):
		self.expression = replacement
		self.match = re.match(self.RE_REPLACE_CORE, replacement)
		self.lookfor = self.match and self.match.group(2)
		self.replacewith = self.match and self.match.group(3)
		self.flags = self.match and self.match.group(4)

		self.bitflags = 0
		self.limit = 1

		for flag in self.flags:
			if flag in self.FLAG_REF:
				self.bitflags = self.bitflags | self.FLAG_REF[ flag ]
			if flag in ('g'):
				self.limit = 0


	def __repr__(self):
		return repr([ self.expression, self.lookfor, self.replacewith, self.flags ])


	def apply(self, string):
		return re.sub(self.lookfor, self.replacewith, string, flags = self.bitflags, count = self.limit)


sample = re.sub(RE_REPLACE_DIRECTIVE, r'\1', sample).strip()
handler = ReplaceParser(sample)

print repr(handler)
# ['s@ABC(\\@2)@\\1DEF@g', 'ABC(\\@2)', '\\1DEF', 'g']

print handler.apply("this is ABC@2 test ABC@2 as well")
# this is @2DEF test @2DEF as well