i talked to harald alvestrand, and he made the good point that the = character is only problematic in URL parameter names. it's ok, if unusual, in parameter values, since the & character is used at the end the value.

apart from that, though, he didn't sound like this would be a priority for the IETF to address. unfortunate, but understandable. :P

so, the resolution here might just be to update the base64 documentation to say that urlsafe_b64encode's output may include the = character. another option would be to change the code to use different character for padding, which would be nicer, but wouldn't follow the spec. up to you.