Python sane does not see scanners

[Nick]

Binary package hint: python-imaging

>>> import sane ; sane.get_devices()
[]

But there are 2 scanners :
$ sane-find-scanner
...
found USB scanner (vendor=0x04a9 [Canon], product=0x221c [CanoScan], chip=GL842) at libusb:001:007
found USB scanner (vendor=0x04f9, product=0x0180) at libusb:003:002

xsane can scan from at least one of them normally.

UPDATE:
And I can scan using device I've got from Xsane, so this works:
>>> import sane ; sane.init() ; sane.open("genesys:libusb:001:007")
<sane.SaneDev instance at 0xb7dcf54c>