[Python-Dev] \u and \U escapes in raw unicode string literals

[M.-A. Lemburg]

On 2007-05-11 07:52, Martin v. Löwis wrote:
>> This is what prompted my question, actually: in Py3k, in the
>> str/unicode unification branch, r"\u1234" changes meaning: before the
>> unification, this was an 8-bit string, where the \u was not special,
>> but now it is a unicode string, where \u *is* special.
> 
> That is true for non-raw strings also: the meaning of "\u1234" also
> changes.
> 
> However, traditionally, there was *no* escaping mechanism in raw strings
> in Python, and I feel that this is a good principle, because it is
> easy to learn (if you leave out the detail that \ can't be the last
> character in a raw string - which should get fixed also, IMO). So I
> think in Py3k, "\u1234" should continue to be a string with 6
> characters. Otherwise, people will complain that
> os.stat(r"c:\windows\system32\user32.dll") fails. Telling them to write
> os.stat(r"c:\windows\system32\u005Cuser32.dll") will just cause puzzled
> faces.

Using double backslashes won't cause that reaction:

os.stat("c:\\windows\\system32\\user32.dll")

Also note that Windows is smart enough nowadays to parse
the good old Unix forward slash:

os.stat("c:/windows/system32/user32.dll")

> Windows path names are one of the two primary applications of raw
> strings (the other being regexes).

IMHO the primary use case are regexps and for those you'd
definitely want to be able to put Unicode characters into your
expressions.

BTW, if you use ur"..." for your expressions today (which you should
if you parse text), then nothing will change when removing the
'u' prefix in Py3k.

-- 
Marc-Andre Lemburg
eGenix.com

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