自作エスケープ処理。想定外のパターンにちゃんとエラーを上げる。

escape.py

# encoding: utf-8

import re

pattern = re.compile(r"""
{0}(?:
  (?P<escaped>{0}) |     # Escape sequence of two delimiters
  (?P<tab>t)       |     # Escape sequence of tab-code
  (?P<cr>r)        |     # Escape sequence of cr-code
  (?P<lf>n)        |     # Escape sequence of lf-code
  (?P<invalid>[^{0}tnr]) # Other ill-formed delimiter exprs
)
""".format(re.escape('\\')), re.IGNORECASE | re.VERBOSE)

def func(mo):
    m = mo.groupdict()
    if m['invalid'] is not None:
        raise SyntaxError('Unknown escape: \\{0}'.format(m['invalid']))
    elif m['tab'] is not None:
        return '\t'
    elif m['cr'] is not None:
        return '\r'
    elif m['lf'] is not None:
        return '\n'
    return '\\'

decoded = pattern.sub(func, r'\\\t\n\r')
print decoded.encode('hex')

末尾にデリミタ来た場合マッチせずスルーしちゃう。そこもエラーで拾いたい場合はもうひと工夫いるかも。