I have a contour generated from SRTM,

How to fill the space between that contour with polygon (for all part) but it generates field in attribute table automaticaly, example in image above between contour 6 and 7 then the polygon generated should have custom field "nilai" with value "6-7" in attribute table.

I've tried polyline to polygon but it's not working I should enter the value of polygon manually, there are so many to be edited one by one.

Please help, any sugestion using python or else. Thanks.