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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 _get_persistent_boot_devices(self):
 """Get details of persistent boot devices, its order :returns: List of dictionary of boot sources and list of boot device order :raises: IloError, on an error from iLO. :raises: IloCommandNotSupportedError, if the command is not supported on the server. """

        # Check if the BIOS resource if exists.
        headers_bios, bios_uri, bios_settings = self._check_bios_resource()

        # Get the Boot resource.
        boot_settings = self._get_bios_boot_resource(bios_settings)

        # Get the BootSources resource
        try:
            boot_sources = boot_settings['BootSources']
        except KeyError:
            msg = ("BootSources resource not found.")
            raise exception.IloError(msg)

        try:
            boot_order = boot_settings['PersistentBootConfigOrder']
        except KeyError:
            msg = ("PersistentBootConfigOrder resource not found.")
            raise exception.IloCommandNotSupportedError(msg)

        return boot_sources, boot_order