Reversing backslashed escape sequences

[Mark Tolonen]

"Steven D'Aprano" <steve-REMOVE-THIS at cybersource.com.au> wrote in message 
news:4c2c2cab$0$14136$c3e8da3 at news.astraweb.com...
>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)

Use 'string-escape':

>>> s=['\\n','\\xff','\\023']
>>> for n in s: n.decode('string-escape')
...
'\n'
'\xff'
'\x13'

-Mark