about bx.intervals.operations.join module #22

Hello.
I am trying to join the genomic intervals of two datasets with bx.intervals.operations.join module.
Two datasets (f1, f2) have chromosome, start, end, and information columns.
My code is like below.
f1 = open( "HIVD1.txt", 'r' )
f2 = open( "HIVD2.txt", 'r' )
f1 = set(f1)
f2 = set(f2)
result = bx.intervals.operations.join.join( f1, f2, mincols=1, leftfill=True, rightfill=False )
result
It just returns <generator object join at 0x1069d2cd0>.
How can I get and see the result?