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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 generate_mask(cls, mask_key, data):
 """ Mask data. :Parameters: mask_key: byte string 4 byte string(byte), e.g. '\x10\xc6\xc4\x16' data: str data to mask """

        # Masking of WebSocket traffic from client to server is required
        # because of the unlikely chance that malicious code could cause
        # some broken proxies to do the wrong thing and use this as an
        # attack of some kind. Nobody has proved that this could actually
        # happen, but since the fact that it could happen was reason enough
        # for browser vendors to get twitchy, masking was added to remove
        # the possibility of it being used as an attack.
        if data is None:
            data = ""

        data = bytearray(data, 'utf-8')

        _m = array.array("B", mask_key)
        _d = array.array("B", data)

        for i in range(len(_d)):
            _d[i] ^= _m[i % 4]

        return _d.tostring()