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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 disks():
    '''
    Return list of disk devices
    '''
    if salt.utils.platform.is_freebsd():
        return _freebsd_geom()
    elif salt.utils.platform.is_linux():
        return _linux_disks()
    elif salt.utils.platform.is_windows():
        return _windows_disks()
    else:
        log.trace('Disk grain does not support OS')