def __init__(self, bus=<NUM_LIT:0>, chip_select=<NUM_LIT:0>, spi_callback=None, speed_hz=<NUM_LIT>):
self.bus = bus<EOL>self.chip_select = chip_select<EOL>self.spi_callback = spi_callback<EOL>self.speed_hz = speed_hz<EOL>self.fd = None<EOL>spi_device = "<STR_LIT>" % (SPIDEV, self.bus, self.chip_select)<EOL>self.open_fd(spi_device)<EOL>
Initialises the SPI device file descriptor.

        :param bus: The SPI device bus number
        :type bus: int
        :param chip_select: The SPI device chip_select number
        :param chip_select: int
        :raises: InitError