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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 pattern(self, pattern):
 """Create a pattern channel. Returns ``_Sender`` object implementing :class:`~aioredis.abc.AbcChannel`. """

        enc_pattern = _converters[type(pattern)](pattern)
        if (enc_pattern, True) not in self._refs:
            ch = _Sender(self, enc_pattern,
                         is_pattern=True)
            self._refs[(enc_pattern, True)] = ch
        return self._refs[(enc_pattern, True)]