basically, you have a series of bills that people have paid -- the question is, who owes whom? this script calculates this, just needs all the receipts and the weights. the weights are, for example, if person x should only pay .5 equal split, weight = .5

split_bill.py

#!/usr/bin/python3 
#Split bills according to payment weights
    #how much each person paid and weight of person
amts={}
while True:
    label=input("\nperson: ")
    if label == "":
        break
    else:
        amt=0
        while True:
            item = input("\t" + label + " receipt paid: ")
            if item == '':
                break
            else:
                amt+=float(item)
        amts[label]={"paid":amt}
        rule = input("\tweight: ")
        if rule == '':
            amts[label]["weight"]=1
        else:
            amts[label]["weight"]=float(rule)

    #calculate difference from what person should pay
#DEBUG for i in amts.items(): print(i)
total = sum([x["paid"] for x in amts.values()])
total_weights=sum([x["weight"] for x in amts.values()])
equal_share_amt = (1 / total_weights) * total
for person in amts.items():
    diff = person[1]["paid"] - (person[1]["weight"] * equal_share_amt)
    amts[person[0]]["diff"]=diff

    #distinguish debts and surpluses
diffs = [[x[0],x[1]["diff"]] for x in amts.items()]
s = sorted([x for x in diffs if x[1] > 0], key=lambda y: y[1])
d = sorted([[x[0], abs(x[1])] for x in diffs if x[1] < 0], key=lambda p: p[1])

     #what people owe generally
for person in diffs:
    if person[1] < 1:
        print("\n{0} owes {1}".format(person[0], round(abs(person[1]),2)))
     
     #what people owe to each person
     #it should be noted that this employs a way to go about this
     #...biggest debtors pay to biggest surplusees, recalculate, etc....
     #however, one can pay off the debts however one wants
while True:
    if not d or not s: break
    else:
        #surplus > debt
        if s[-1][1] > d[-1][1]:
            print("\t\t{0} owes {1} {2} dollars".format(d[-1][0], s[-1][0], round(d[-1][1],2)))
            s[-1][1] =  s[-1][1] - d[-1][1]
            del d[-1]

        #surplus == debt
        elif s[-1][1] == d[-1][1]:
            print("\t\t{0} owes {1} {2} dollars".format(d[-1][0], s[-1][0], round(d[-1][1],2)))
            del d[-1]
            del s[-1]
       
        #surplus < debt
        else:
            print("\t\t{0} owes {1} {2} dollars".format(d[-1][0], s[-1][0], round(s[-1][1],2)))
            d[-1][1] =  d[-1][1] - s[-1][1]
            del s[-1]