unicode input produces ValueError which crashes clients

[adobeDan]

If you are running in Python 2, and you pass in a (unicode) email or username that contains a non-ascii character, the ValueError that's thrown contains a py2 str message with that non-ascii character, instead of a unicode message containing the actual email or username. This message cannot be formatted by clients, because they can't know the encoding, and in py3 it's not valid.

[adobeDan]

This fix doesn't actually work for all clients, because part of the contract of ValueError is that you can call str on it, but the built-in str command for Exception doesn't handle unicode.

[adobeDan]

Solution is to create ArgumentError a subclass of ValueError which, only in py2, encodes any uncode error message using utf8 so it's guaranteed to be a str. Since this is a subclass of ValueError, it's backward compatible with the existing API for any clients that are catching ValueError.