class BF(object)
   def __init__():
   .
   .
   def add(self,z):
   .
   .

from y import BF
def FUNC((a,b,bf))
   .
   .
   bf.add(x)
   .
   .
   return bf

.
.
if __name__ == '__main__':
    pool = multiprocessing.Pool(3)
    for i in range(len(sl)):
         bf_set.append(BF())
    results = pool.map(FUNC,zip(sl, itertools.repeat(aa), bf_set))

PicklingError: Can't pickle <type 'instancemethod'>: attribute lookup __builtin__.instancemethod failed