Reversing backslashed escape sequences

[Chris Rebert]

On Wed, Jun 30, 2010 at 10:50 PM, Steven D'Aprano
<steve-REMOVE-THIS at cybersource.com.au> wrote:
> I have a byte-string which is an escape sequence, that is, it starts with
> a backslash, followed by either a single character, a hex or octal escape
> sequence. E.g. something like one of these in Python 2.5:
>
> '\\n'
> '\\xFF'
> '\\023'
>
> If s is such a string, what is the right way to un-escape them to single
> character byte strings?
>
> I could decode them to unicode first, then encode to ASCII:
>
>>>> s = '\\n'
>>>> assert len(s) == 2
>>>> s.decode('unicode-escape').encode()
> '\n'
>
> but this fails for non-ASCII bytes:
>
>>>> '\\xFF'.decode('unicode-escape').encode()
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> UnicodeEncodeError: 'ascii' codec can't encode character u'\xff' in
> position 0: ordinal not in range(128)

Python 2.6.5 (r265:79063, May 25 2010, 18:21:57)
>>> '\\xFF'.decode('string_escape')
'\xff'

Cheers,
Chris
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