doubling slashes in a string

[Alex Martelli]

"Remco Gerlich" <scarblac at pino.selwerd.nl> wrote in message
news:slrn8u3i4t.fgl.scarblac at pino.selwerd.nl...
> Alex Martelli <aleaxit at yahoo.com> wrote in comp.lang.python:
> > Whoops!  You're right.  I had never noticed this lexical peculiarity,
> > and now I wonder about the rationale for it -- since backslashes play
> > no special role within a rawstring, why the peculiarly specific
prohibition
> > about having an odd number of them _at the end_...?
>
> They still have a special role - they escape quotes. r"\"" still needs
> to be equal to '"'.

If r"\"" really needs to be equal to '"', then we're in serious trouble,
at least in Python 2.0:

Python 2.0b2 (#6, Sep 26 2000, 14:59:21) [MSC 32 bit (Intel)] on win32
Type "copyright", "credits" or "license" for more information.
IDLE 0.6 -- press F1 for help
>>> r"\""
'\\"'
>>>

i.e., r"\"" rather seems to be equal to \\\".

Still, you're right, that quote IS playing a role -- it inserts itself
in the string AND also inserts the following quoting-character (while,
without the \, said following quoting-character would otherwise terminate
the rawstring).  Whether it "should" do either or both things is moot,
it definitely IS doing them both.


> As a consequence, a single \ at the end of a raw
> string always escapes the quote, so the string isn't closed.

Yep, pretty clear now.


> > Oh well, then I guess my above-quoted suggestions will have to be
reworded:
> >
> >     newname = oldname.split('\\').join(r'\\')
> >     newname = oldname.replace('\\', r'\\')
>
> Note that if he's doing things with pathnames on Windows, it might
> be a lot easier to use / instead of \ to start with (that works).

I think the original poster explained that he needs to prepare a
string to be passed to another program (dunno if by system, popen,
or what else), so he *cannot* assume that / will work just the
same as \ (on the commandline of many DOS and Windows programs,
the equivalence does not hold).  I guess the doubling is what he
needs to protect the backslashes from one level of stripping
(whoever may be doing that...).


Alex