def prepare_choice_list(keys_QuerySet, values_QuerySet, foreignKey_field, localKey_field):
# gets the values of the FK in the model as a list of tuples in the form:
# [(row1_FKValue,),(row2_FKValue,),...]
# uses distinct() to not repeat values in the option list
        a = keys_QuerySet.distinct().values(foreignKey_field)

#and then expand the tuples in a single list of elements
	a = [v[foreignKey_field] for v in a]

	b = []

	for v in a:

# search the "human readable" values in the related model 
# for the keys before extracted
		bs = eval("values_QuerySet.get(%s__iexact = '%s').__unicode__()"%(localKey_field,v))

		b.append(bs)

#inserts a empty option as the default (first) option in the select
#just comment the two lines below if you don't want it
	a.insert(0,"")
	b.insert(0,"----------")

# the zip funtions joins two lists in the form [(list1_value, list2_value),...]
	return zip(a,b)