Back Slash not allowed at the end of raw string?

[yuhao]

I'm using Python 2.5 on Windows XP Pro.
While testing for strings, I got the following result:

>>> r'c:\'
SyntaxError: EOL while scanning single-quoted string

>>> r'c:\nwin'
'c:\\nwin'

>>> r"c:\"
SyntaxError: EOL while scanning single-quoted string

>>> r'\n'
'\\n'

>>> r'\"'
'\\"'

It seemed that when a back slash is inside the raw string, 
it is correctly recognized as a normal character, not translated; 
but when put to the end, it raise an error.

And the message looks so strange:

>>> r"c:\"
SyntaxError: EOL while scanning single-quoted string


what does this message mean? I'm not using any single quote in the statement.
It this a bug or by design?
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