A sample bill program

biller.py

from __future__ import print_function

def calculate_bill_amount(gem_list, price_list, reqd_gems, reqd_quantity):
    bill_amount = -1
    gem_dict = dict(zip(gem_list, price_list))
    order_dict = dict(zip(reqd_gems, reqd_quantity))

    for gem in reqd_gems:
        if not gem_dict.get(gem):
            return bill_amount

    for gem in reqd_gems:
        bill_amount = bill_amount + gem_dict[gem] * order_dict[gem]

    print(bill_amount)
    if bill_amount > 30000:
        bill_amount = bill_amount * 0.95

    return bill_amount

gem_list = ["Emerald", "Ivory", "Jasper", "Ruby", "Garnet"]
price_list = [1760, 2119, 1599, 3920, 3999]

reqd_gems = ["Ivory", "Emerald", "Garnet"]
reqd_quantity = [3, 10, 2]

bill_amount = calculate_bill_amount(gem_list, price_list, reqd_gems, reqd_quantity)
print(bill_amount)