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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def prefixes(self, key):
        '''
        Returns a list with keys of this DAWG that are prefixes of the ``key``.
        '''
        res = []
        index = self.dct.ROOT
        if not isinstance(key, bytes):
            key = key.encode('utf8')

        pos = 1

        for ch in key:
            index = self.dct.follow_char(int_from_byte(ch), index)
            if not index:
                break

            if self._has_value(index):
                res.append(key[:pos].decode('utf8'))
            pos += 1

        return res