Handle Unicode for Incoming Keys

Kindly review my code
@adampalay  @zubair-arbi @waheedahmed @symbolist 
We generally prefer to pass a format string and args instead of a pre-formatted string to log functions. So this should be:
`log.exception("Invalid key %s", key)`

http://stackoverflow.com/questions/11955787/idiomatic-python-logging-format-string-args-list-vs-inline-string-formatting