"""Optional fixer that changes all unprefixed string literals "..." to b"...".

br'abcd' is a SyntaxError on Python 2 but valid on Python 3.

ur'abcd' is a SyntaxError on Python 3 but valid on Python 2.

"""

from __future__ import unicode_literals

import re

from lib2to3.pgen2 import token

from lib2to3 import fixer_base

_literal_re = re.compile(r"[^bBuUrR]?[\'\"]")

class FixBytes(fixer_base.BaseFix):

BM_compatible = True

PATTERN = "STRING"

def transform(self, node, results):

if node.type == token.STRING:

if _literal_re.match(node.value):

new = node.clone()

new.value = u'b' + new.value

return new