"""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__importunicode_literalsimportrefromlib2to3.pgen2importtokenfromlib2to3importfixer_base_literal_re=re.compile(r"[^bBuUrR]?[\'\"]")classFixBytes(fixer_base.BaseFix):BM_compatible=TruePATTERN="STRING"deftransform(self,node,results):ifnode.type==token.STRING:if_literal_re.match(node.value):new=node.clone()new.value=u'b'+new.valuereturnnew