backslash plague

[Bengt Richter]

On Sat, 23 Oct 2004 22:33:05 GMT, bokr at oz.net (Bengt Richter) wrote:

>On Fri, 22 Oct 2004 21:20:30 +0200, aleaxit at yahoo.com (Alex Martelli) wrote:
>
>>Luis P. Mendes <luisXX_lupe2XX at netvisaoXX.pt> wrote:
>>    ...
>>> I've already read many pages on this but I'm not able to separate the
>>> string 'R0\1.2646\1.2649\D' in four elements, using the \ as the separator.
>>
>>x = r'R0\1.2646\1.2649\D'
>>elements = x.split('\\')
>>
>>> and why must I write two '' after the \?  If I hadn't used r I would
>>> understand...
>>
>>A raw literal can't end with an odd number of backslashes (_some_ way
>>has to be there to escape the quote char, after all).
>>
>Hm, just had the thought that something analogous to HDLC bit-stuffing
>could be used. IIRC bitstreams had escape flags composed of 5 successive bits,
>and if you wanted to transmit 5 successive data bits, you just added an extra bit
>at the end to make 6 to show that the five did not comprise a flag. The extra bits
>would get dropped on decoding when a 6th 1 followed 11111 and would be recognized
>as a flag otherwise.
BZZT! wrong ;-(
The flag is 01111110 and I believe 0 gets stuffed after the 5th 1 to make sure
the flag is not part of data between real flags.

>
>Translating this to quoted character sequences, we could have an alternate triple
>quoted raw string format, with quote-stuffing instead of escapes. I.e., to quote
>three successive quote characters, we stuff a 4th quote, which the tokenizer drops
>as it creates the internal byte sequence string representation, so we don't need
>escapes in the usual sense.
This does not work for e.g. quoting as single quote, so it's not general at all :-(

>
>Thus (using f prefix to indicate flagged quote-stuffing syntax) you could write:
>
>    x = f'''c:\whatever\'''
>
>and to quote the line above (without taking advantage of alternate quotes):
>
>    q = f'''    x = f''''c:\whatever\'''''''
>         ^^^         ^^^|            ^^^|^^^
>
>where ^^^ is flag and | indicates a stuffed quote that
>makes the previous otherwise-flag into three quotes in the data.
>You could quote again (using same type quote for illustrative purposes
>again, since oviously you could do better using both ' and "):
>
>    r = f'''f''''    x = f'''''c:\whatever\'''''''''''
>             ^^^|         ^^^|             ^^^|^^^|^^^
>
>(I think ;-)
>
>I guess the worst-case data to quote would be a repeating pattern of
>'''""" or """''' since neither type of quote character would give an
>advantage, but 1-in-6 overhead is still not too bad, and it would be rare.
>
>Is there a hole in this raw string quoting syntax?
>
Unfortunately, yes.

I thought of another format, but it doesn't quote previously quoted arbitrary text
without modifying at least the last character, so phooey. Might as well go to the
previously suggested mime-style delimiting, which an editor macro could do for
arbitrary selected text. It could use str(time.time()) as delimiter text without
much risk, IWT.

Regards,
Bengt Richter