Returns list of other keys that are mapped to the same value as specified key. 
            @param key - key for which other keys should be returned.
            @param including_current if set to True - key will also appear on this list.

def get_other_keys(self, key, including_current=False):
        """ Returns list of other keys that are mapped to the same value as specified key. 
            @param key - key for which other keys should be returned.
            @param including_current if set to True - key will also appear on this list."""
        other_keys = []
        if key in self:
            other_keys.extend(self.__dict__[str(type(key))][key])
            if not including_current:
                other_keys.remove(key)
        return other_keys