[Tutor] Question about the raw string

[Steven D'Aprano]

On Wed, Nov 28, 2012 at 01:01:12AM +0000, JiangShan wrote:
> Hi everyone, 
> 
>        I am studying the python 3 and I am confused about the raw 
>        string. Why does the python interpreter do not escape the 
>        single backslash before the quotes even I add a "r" before the 
>        string.  The following is an example:
>
>        >>> print(r"\")
>       
>         SyntaxError: EOL while scanning string literal
>        >>> print(r"\\")
>         \\
>         >>> 

A very good question! Note that this is not just in Python 3, the same 
thing applies to all versions of Python, and even other implementations 
like IronPython:

steve at runes:~$ ipy
IronPython 2.6 Beta 2 DEBUG (2.6.0.20) on .NET 2.0.50727.1433
Type "help", "copyright", "credits" or "license" for more information.
>>> s = r"\"
  File "<stdin>", line 1
    s = r"\"

        ^
SyntaxError: EOL while scanning single-quoted string



Unfortunately, there is no good answer except "that's the way it is, 
because that's the way the string parser is designed to work". It is a 
documented limitation of raw strings:

http://docs.python.org/2/reference/lexical_analysis.html#string-literals

and it has been reported as a bug but closed as "Invalid":

http://bugs.python.org/issue1271



-- 
Steven