Python 3.4：试图让这个模块对这个2d数组中的销售总数求和。不工作

def sales_per_zip(sales):
    sales_sum = 0
    i = 1
    print(sales[1][0])
    zipcode = input("Enter the Zip Code here:")
    if zipcode == sales[1][0]:
        while i <= 6:
            sales_sum =+ sales[1][i]
            i =+ 1
            print(i)

    print(sales_sum)

sales = [
["Zip Code", "Mocha", "Latte", "Regular", "Decaf", "Caramel"],
[48093,180,100,200,180,150],
[48088,270,330,160,150,250],
[48026,240,310,450,100,320],
[48066,200,230,350,110,360],
]
opt = ""

print("What would you like to do?")
print("Z = Get Total Sales by Zip Code.")
print("C = Get Total Sales by Coffee Type.")
print("G = Get Grand Total of all Coffee Sales.")
print("HZ = Get Highest Sales by Zip Code.")
print("HC = Get Highest Sales by Coffee Type.")
opt = str(input("Enter your option here:"))

if opt == "z" or opt == "Z":
    sales_per_zip(sales)
#elif opt == "c" or opt == "C":
#
#elif opt == "g" or opt == "G":
#
#elif opt == "hz" or opt == "HZ":
#
#elif opt == "hc" or opt == "HC":
def sales_per_zip(sales):
    sales_sum = 0