using re module to find

[anton]

John Machin <sjmachin <at> lexicon.net> writes:

> 
> On Jun 12, 7:11 pm, anton <anto... at gmx.de> wrote:
> > Hi,
> >
> > I want to replace all occourences of " by \" in a string.
> >
> > But I want to leave all occourences of \" as they are.
> >
> > The following should happen:
> >
> >   this I want " while I dont want this \"

... cut text off 
> What you want is:
> 
> >> import re
> >> text = r'frob this " avoid this \", OK?'
> >>> text
> 'frob this " avoid this \\", OK?'
> >> re.sub(r'(?<!\\)"', r'\"', text)
> frob this \\" avoid this \\", OK?'
> >>
> 
> HTH,
> John
> --
> http://mail.python.org/mailman/listinfo/python-list
> 
> 


First.. thanks John.

The whole problem is discussed in

http://docs.python.org/dev/howto/regex.html#the-backslash-plague

in the section "The Backslash Plague"

Unfortunately this is *NOT* mentioned in the standard
python documentation of the re module.

Another thing which will always remain strange to me, is that
even if in the python doc of raw string:

http://docs.python.org/ref/strings.html

its written:
   "Specifically, a raw string cannot end in a single backslash"

s=r"\\"  # works fine
s=r"\"   # works not (as stated)

But both ENDS IN A SINGLE BACKSLASH !

The main thing which is hard to understand is:

If a raw string is a string which ignores backslashes,
then it should ignore them in all circumstances,

or where could be the problem here (python parser somewhere??).

Bye

  Anton