Running help() or mktemp() causes _getfullpathname to be called with the whole system path (791 characters). If you pass that to _getfullpathname as str it throws the aforementioned TypeError. If it's passed as unicode, it returns an empty string.
The offending _getfullpathname call occurs on the first call to one of these methods. Future calls to either do not call it (unless, of course, the first failed).