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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 devno_alloc(self):
 """ Allocates a device number unique to this partition, in the range of 0x8000 to 0xFFFF. Returns: string: The device number as four hexadecimal digits in upper case. Raises: ValueError: No more device numbers available in that range. """

        devno_int = self._devno_pool.alloc()
        devno = "{:04X}".format(devno_int)
        return devno