Stand-alone sample code for converting some three-character octal escapes in Route 53 DNS domain names to their equivalent low-ASCII characters.

route53octals.py

#!/usr/bin/python
# coding: utf-8

import re, unittest

def octalReplace(x):
    c = int(x.group(1), 8)
    if c > 0x20 and c < 0x2e or c > 0x2e and c < 0x7f:
        return chr(c)
    else:
        return x.group(0)

def prettyDnsName(value):
    return re.sub(r'\\(\d{3})', octalReplace, value)

class DecodeSomeOctalEscapesTest(unittest.TestCase):
    def testShouldNotDecodeSmallLetterUWithDiaeresis(self):
        # fübar
        self.assertEqual(r'f\374bar', prettyDnsName(r'f\374bar'))

    def testShouldNotDecodePeriod(self):
        # f.bar
        self.assertEqual(r'f\056bar', prettyDnsName(r'f\056bar'))

    def testShouldDecodeAsterisk(self):
        self.assertEqual('*.foo', prettyDnsName(r'\052.foo'))

    def testShouldDecodeSmallLetterU(self):
        self.assertEqual('fubar', prettyDnsName(r'f\165bar'))

if __name__ == '__main__':
    unittest.main()