[Python-Dev] Raw string syntax inconsistency

[Guido van Rossum]

Would it make sense to detect and reject these in 3.3 if the 2.7 syntax is
used?

--Guido van Rossum (sent from Android phone)
On Jun 17, 2012 1:13 PM, "Nick Coghlan" <ncoghlan at gmail.com> wrote:

> On Mon, Jun 18, 2012 at 3:54 AM, Terry Reedy <tjreedy at udel.edu> wrote:
> > The premise of the discussion of adding 'u', and of Guido's acceptance,
> was
> > that "it's about as harmless as they come". I do not remember any
> discussion
> > of 'ur' and what it really means in 2.x, and that supporting it meant
> adding
> > back 2.x's interaction effect. Indeed, Nick's version goes on to say
> "This
> > PEP was originally written by Armin Ronacher, and Guido's approval was
> given
> > based on that version." Armin's original version (and subsequent edit)
> only
> > proposed adding 'u' (and 'U') and made no mention of 'ur'. Nick's
> seemingly
> > innocuous addition of also adding 'ur' came after Guido's approval, and
> as
> > discovered, is not so innocuous.
>
> Right, that matches my recollection as well - we (or least I) thought
> mapping "ur" to the Python 3 "r" prefix was sufficient, but it turns
> out doing so means there are some 2.x string literals that will
> silently behave differently in 3.x.
>
> Martin's right that that part of the PEP should definitely be amended
> (along with the relevant section in What's New)
>
> > I do not think he needs to discuss adding and deleting support, but
> merely
> > state that 'ur' support is not added because 'ur' has a special meaning
> that
> > would require changing literal handling. The sentence about supporting
> 'ur'
> > could be negated and moved after the sentence about not changing Unicode
> > handling. A possibility:
> >
> > "Combination of the unicode prefix with the raw string prefix will not be
> > supported because in Python 2, the combination 'ur' has a special meaning
> > that would require changing the handling of unicode literals"
>
> In addition to changing the proposal section to only cover "u" and
> "U", I'll actually add a new subsection along the lines of the
> following:
>
> Exclusion of Raw Unicode Strings
> -------------------------------------------------
>
> Python 2.x includes a concept of "raw Unicode" strings. These are
> partially raw string literals that still support the "\u" and "\U"
> escape codes for Unicode character entry, but otherwise treat "\" as a
> literal backslash character. As 3.x has no such concept of a partially
> raw string literal, explicit raw Unicode literals are still not
> supported. Such literals in Python 2 code will need to be converted to
> ordinary Unicode literals for forward compatibility with Python 3.
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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