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

[M.-A. Lemburg]

On 2007-05-11 00:11, Guido van Rossum wrote:
> On 5/10/07, M.-A. Lemburg <mal at egenix.com> wrote:
>> On 2007-05-10 20:53, Paul Moore wrote:
>>> On 10/05/07, Guido van Rossum <guido at python.org> wrote:
>>>> I just discovered that, in all versions of Python as far back as I
>>>> have access to (2.0), \uXXXX escapes are interpreted inside raw
>>>> unicode strings. Thus:
>>> [...]
>>>> Does anyone remember why it is done this way? The reference manual
>>>> describes this behavior, but doesn't give an explanation:
>>> My memory is so dim as to be more speculation than anything else, but
>>> I suspect it's simply because there's no other way of including
>>> characters outside the ASCII range in a raw string.
>> This is per design (see PEP 100) and was done for the reason given
>> by Paul. The motivation for the chosen approach was to make Python's
>> raw Unicode strings compatible to Java's raw Unicode strings:
>>
>> http://java.sun.com/docs/books/jls/second_edition/html/lexical.doc.html
> 
> I'm not sure what Java compatibility buys us. It is also far from
> perfect -- IIUC, in Java if you write \u0022 (that's the " character)
> it counts as an opening or closing quote, and if you write \u005c (a
> backslash) it can be used to escape the following character. OTOH, in
> Python, you can write ur"C:\Program Files\u005c" and voila, a raw
> string terminating in a backslash. (In Java this would escape the "
> instead.)

http://mail.python.org/pipermail/python-dev/1999-November/001346.html
http://mail.python.org/pipermail/python-dev/1999-November/001392.html
and all the other postings in that month related to this.

> However, I understand the other reason (inclusion of non-ASCII
> characters in raw strings) and I reluctantly agree with it.
> Reluctantly, because it means I can't create a raw string containing a
> \ followed by u or U -- I needed one of those today.

>>> print ur"\u005cu"
\u

-- 
Marc-Andre Lemburg
eGenix.com

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