1"""Optional fixer that changes all unprefixed string literals "..." to b"...".
2
3br'abcd' is a SyntaxError on Python 2 but valid on Python 3.
4ur'abcd' is a SyntaxError on Python 3 but valid on Python 2.
5
6"""
7from __future__ import unicode_literals
8
9import re
10from lib2to3.pgen2 import token
11from lib2to3 import fixer_base
12
13_literal_re = re.compile(r"[^bBuUrR]?[\'\"]")
14
15class FixBytes(fixer_base.BaseFix):
16    BM_compatible = True
17    PATTERN = "STRING"
18
19    def transform(self, node, results):
20        if node.type == token.STRING:
21            if _literal_re.match(node.value):
22                new = node.clone()
23                new.value = u'b' + new.value
24                return new
25