Unable to do Duplex Scanning

Hi, I am trying to do duplex scanning using Python-sane but unable to do duplex scanning please help me ... regards

import scanPython
from PIL import  Image

mode = 'grey'

var = scanPython.init()
print("sane version ", var)
devices = scanPython.get_devices()
print('Available devices:', devices)

dev = scanPython.open(devices[0][0])
dev.__setattr__(2,'ADF Duplex') 
print("Current Source",dev.__getattr__(2))
dev.set_mode =mode
dev.resolution = 200
dev.start()
iterator = dev.multi_scan()
progress = True

while progress:
    try:
        image = iterator.next()
 except:
        progress = False
        break
#dev.cancel()

dev.close()

Start by reproducing the reported flow through scanPython.init, get_devices, open, the source selection, and multi_scan with a duplex-capable scanner. Check whether the interface exposes duplex scanning and whether the iterator returns both sides; done means documenting the supported behavior or identifying a reproducible library defect with the device details and error.