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This occurs even when calling methods in modules (such as os.path.splitext), so I know it's not happening due to an error on my part
Win7 SP1

You'll have to give more details about what you are doing, but I suspect you are in fact calling it incorrectly. In addition, there are pretty much no circumstances in which you want to use string.rfind in 2.7. Just use ''.rfind.

Ah, perhaps you *meant* you are calling rfind on a string, rather than calling rfind on the 'string' module as I imagined.
So, we definitely need more details about how you are producing this failure and what the traceback looks like. 'abc'.rfind('a') works fine for me, and works fine on Windows in our unit tests.

Sorry about the lack of clarity there.
I'm calling os.path.splitext("C:\blah.ext") and trackback is returning an AttributeError: 'list' object has no attribute 'rfind' from within the definition for splitext in the NTPath module.
That's only the specific usage that brought about the error - I'm getting it for all calls to rfind everywhere.
I will admit it's a very strange error - I did some searching around and nobody else is experiencing the bug, so clearly it's a problem with my particular installation of Python. I haven't used any third-party Python extensions, however, and everything seems like it's as vanilla as possible to me.

I can't reproduce this. Can you please post the entire traceback? It would be preferable if you could also show the exact code that's causing the problem, typed from a python command prompt (see my example below).
I can reproduce the error if I pass a list to ps.path.splitext(), which is what I suspect you're doing:
>>> os.path.splitext(['c:\\blah.ext'])
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/usr/lib/python2.6/posixpath.py", line 95, in splitext
 return genericpath._splitext(p, sep, altsep, extsep)
 File "/usr/lib/python2.6/genericpath.py", line 91, in _splitext
 sepIndex = p.rfind(sep)
AttributeError: 'list' object has no attribute 'rfind'
And you probably want: os.path.splitext("C:\\blah.ext"), so as to escape the backslash.

I'm going to close this. Feel free to re-open it if you can give a small example showing the problem.

Actually, I did some diagnosis and it would appear it was actually an inappropriate call - I was assuming os.path.walk returned a tuple containing a list of files instead of a tuple containing a list of lists of files.
Sorry about that.