遍历元组列表

Question

I have a list of a tuples and I want to iterate through it and calculate the total cost. I want to get the total cost of orange plus the total cost of the banana. For example, 5.26*8 + 2.00* 10 to find out the total cost.

How do I access these values? I try to access for example 5.26 using b[1]*b[2] but I get an error.

def totalcost(shoping):
    for a in shoping:
        for b in a:
        total1=b[1]*b[2]
        print(total1)

shoping=[("orange",5.26,8),("banana",2.00,10)]
totalcost(shoping)

Answer 1

One way is to unpack each tuple into three variables:

def get_total_cost(shopping):
    total_cost = 0
    for line_item in shopping:
        product, cost, quantity = line_item  # Unpack the tuple
        total_cost += quantity * cost
    return total_cost

shopping=[("orange", 5.26, 8), ("banana", 2.00, 10)]
print(get_total_cost(shopping))

One can combine the unpacking with the loop:

def get_total_cost(shopping):
    total_cost = 0
    for product, cost, quantity in shopping:
        total_cost += quantity * cost
    return total_cost

It is possible to write the entire computation as a single generator expression :

def get_total_cost(shopping):
    return sum(quantity * cost for product, cost, quantity in shopping)

I gave product a name for clarity. However, in code like this it is customary to see _ in place of unused variables:

def get_total_cost(shopping):
    return sum(quantity * cost for _, cost, quantity in shopping)

For completeness, I'll mention that it is possible to access tuple elements by index:

    return sum(line_item[1] * line_item[2] for line_item in shopping)

though to my eye this is significantly less readable than using named variables.

Finally, if you're on Python 3.7 ( or 3.6 ) you should consider using dataclasses . If you're using an earlier version of Python, collections.namedtuple is an option.

Answer 2

You have tuple in for loop in a so you can slice values from that tuple.

def totalcost(shoping):
    for a in shoping:
        total1=a[1]*a[2]
        print(total1)

shoping=[("orange",5.26,8),("banana",2.00,10)]
totalcost(shoping)