如何从元组的元组中提取值

Question

I have list of this sort. It is the order list of a person:

orderList  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]
#Here the second value is the quantity of the fruit to be purchased

How do I extract the string and the float value separately? I need to calculate the total order cost based on the given fruit prices:

fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75,
              'limes':0.75, 'strawberries':1.00}

This is what I have tried:

def buyLotsOfFruit(orderList):
    """
        orderList: List of (fruit, numPounds) tuples

    Returns cost of order
    """
    totalCost = 0.0
    length = len(orderList)
    for i in range(0,length):
        for j in range(0, length - i - 1):
            totalCost += fruitPrices[orderList[i]] * orderList[j]
    return totalCost

This yields wrong answer. What am I doing wrong? How can I fix this?

Thanks!

Answer 1

You might use unpacking together with for loop to get easy to read code, for example

orderList  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]
fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75,
              'limes':0.75, 'strawberries':1.00}
total = 0.0
for name, qty in orderList:
    total += qty * fruitPrices[name]
print(total)  # 12.25

Note , inside for ... in so name values become 1st element of tuple and qty becomes 2nd element of tuple.

Answer 2

Just iterate the list of tuple, and multiply each quantity with their price and pass the iterator to sum function to get total

total = sum(qty*fruitPrices.get(itm,0) for itm,qty in orderList)
# 12.25

Answer 3

How about?

orderList  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]

fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75,
              'limes':0.75, 'strawberries':1.00}

order_total = 0.00

You can iterate over the list of tuples and use name to get the fruit name and quantity to get the quantity. Using that you can look up the price value of the fruit from the fruitPrices dictionary using the key and multiple by the quantity, totalling as you go:

for name, quantity in orderList:
    order_total += fruitPrices.get(name, 0) * quantity

print(order_total)

Then into your function would look like this:

orderList  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]

fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75,
              'limes':0.75, 'strawberries':1.00}

def buyLotsOfFruit(orderList):
    """
        orderList: List of (fruit, numPounds) tuples

    Returns cost of order
    """
    totalCost = 0.0
    for name, quantity in orderList:
        totalCost += fruitPrices.get(name, 0) * quantity
    return totalCost

print(buyLotsOfFruit(orderList))

Answer 4

I change your code to don't get any errors.

Your orderList is tuple you can accese each fruit_name with [i][0] and count with [i][1] and for searching in dict you can use dict.get(searching_key, value if not fount) , You can change default value to any value you like, I set zero.

def buyLotsOfFruit(orderList, fruitPrices):
    totalCost = 0.0
    length = len(orderList)
    for i in range(0,length):
        totalCost += fruitPrices.get(orderList[i][0], 0) * orderList[i][1]
    return totalCost

buyLotsOfFruit(orderList, fruitPrices)

You can use functools.reduce to summarize your code.

>>> from functools import reduce
>>> reduce(lambda x,y : x+fruitPrices.get(y[0],0)*y[1], orderList, 0)
12.25

---

12.25

Answer 5

def buyLotsOfFruit(orderList, fruitPrices):
    totalCost = 0.0
    for order in orderList:
        item, quantity = order
        item_price = fruitPrices[item]
        totalCost += (item_price * quantity)
    return totalCost

Answer 6

Code:

order_list  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]
fruit_prices = {'apples': 2.00, 'oranges': 1.50, 'pears': 1.75, 'limes': 0.75, 'strawberries': 1.00}


def buyLotsOfFruit(order_list, fruit_prices):
    total_cost = 0
    for i in order_list:
        total_cost += fruit_prices[i[0]] * i[1]
    return total_cost


print(buyLotsOfFruit(order_list, fruit_prices))

Output:

12.25

Okay, so here is some explanation.

1. Instead of getting the length of list we can just pass it and python will iterate over it's elements automaticly.
   for i in order_list:
2. i is the current tuple in order_list eg: [('apples', 2.0) . So we can access it this way: i[0] , we get apples . And we use string apples to access apples price, you can imagine it this way: fruit_prices["apples"] , and so we have price.
3. We get the amount we want, we use i[1] which returns 2.0 in our exmaple with apples.

So you can image it looking like this:

total_cost += price * amount

And also we could do

total_cost = total_cost + price * amount

but you can also use += operator to simplify the expression.

Answer 7

Try this:

def buyLotsOfFruit(orderList):
    """
        orderList: List of (fruit, numPounds) tuples

    Returns cost of order
    """
    fruitPrices = {'apples': 2.00, 'oranges': 1.50, 'pears': 1.75,
                   'limes': 0.75, 'strawberries': 1.00}

    totalCost = 0.0

    for item in orderList:
        fruit, price = item[0], item[1]
        totalCost += price

    return totalCost


if __name__ == '__main__':
    print(buyLotsOfFruit(orderList=[('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]))  # 9.0

Answer 8

To fully understand and visualise your data, you can use pandas:

import pandas as pd

orderList  = [('apples', 2.0), ('pears', 3.0), ('limes', 4.0)]
fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75,
              'limes':0.75, 'strawberries':1.00}
df = pd.DataFrame(orderList, columns = ['fruit', 'quantity'])
df['cost'] = df.apply( lambda row: row.quantity * fruitPrices[row.fruit], axis=1)
df

This returns:

fruit   quantity    cost
0   apples  2.0     4.00
1   pears   3.0     5.25
2   limes   4.0     3.00

To get total cost: df['cost'].sum()