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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_mode(device_filter):
 """Determine which beacons the scanner should look for."""

    from .device_filters import IBeaconFilter, EddystoneFilter, BtAddrFilter, EstimoteFilter
    if device_filter is None or len(device_filter) == 0:
        return ScannerMode.MODE_ALL

    mode = ScannerMode.MODE_NONE
    for filtr in device_filter:
        if isinstance(filtr, IBeaconFilter):
            mode |= ScannerMode.MODE_IBEACON
        elif isinstance(filtr, EddystoneFilter):
            mode |= ScannerMode.MODE_EDDYSTONE
        elif isinstance(filtr, EstimoteFilter):
            mode |= ScannerMode.MODE_ESTIMOTE
        elif isinstance(filtr, BtAddrFilter):
            mode |= ScannerMode.MODE_ALL
            break

    return mode