<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _fix_key(key):
        '''Normalize keys to Unicode strings.'''
        if isinstance(key, unicode):
            return key
        if isinstance(key, str):
            # On my system, the default encoding is `ascii`, so let's
            # explicitly say UTF-8?
            return unicode(key, 'utf-8')
        raise TypeError(key)