HTTPError doesn't have a reason attribute
Whenever the login fails I get an exception: "AttributeError: can't set attribute" in the following line:
self.reason = args["Error"]
This is rietveld.py trying to create a ClientLoginError() instance. See http://bugs.python.org/issue13211, in Python 2.7 urllib2.HTTPError doesn't have a reason attribute. You obviously "inherited" that issue from rietveld's upload.py, not sure whether rietveld fixed it by now however.