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:
'\n'

but this fails for non-ASCII bytes:
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)

 

[Chris Rebert]

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:

'\n'

but this fails for non-ASCII bytes:

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'

Cheers,
Chris

 

[Mark Tolonen]

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:

'\n'

but this fails for non-ASCII bytes:

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

 

[Steven D'Aprano]

Python 2.6.5 (r265:79063, May 25 2010, 18:21:57)
'\xff'

I knew unicode-escape, obviously, and then I tried just 'escape', but
never thought of 'string_escape'.

Thanks for the quick answer.