Reversing backslashed escape sequences

[Steven D'Aprano]

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)





-- 
Steven