Python: Multiplying numbers in a list of tuples and totalling it

Question

I'm trying to create a code where the first two numbers of a tuple are multiplied, and then totaled with other tuples. Here's my very wonky code:

numbers = [(68.9, 2, 24.8),
             (12.4, 28, 21.12),
             (38.0, 15, 90.86),
             (23.1, 45, 15.3),
             (45.12, 90, 12.66)]

def function(numbers):

    first_decimal = [element[1] for element in numbers]
    integer = [element[2] for element in numbers]

    string_1 = ''.join(str(x) for x in first_decimal)
    string_2 = ''.join(str(x) for x in integer) 
    # It says 'TypeError: float() argument must be a string or a number',
    # but doesn't this convert it to a string??

    tot = 1
    for element in first_decimal:
        tot = float(first_decimal) * int(integer)

    return tot

function(numbers)

Forgot about the output. So basically what is needed is the total of:

total_add =  68.9 + 2, 12.4 + 28, 23.1 + 45, 45.12 + 90

ie the first two numbers of every tuple in the list. Apologies.

Answer 1

If you literally want to add up the product of the first two elements in each tuple, then you can use the sum() function with a generator:

>>> sum(t[0] * t[1] for t in numbers)
6155.299999999999

which we can check is correct through the following

>>> 68.9 * 2 + 12.4 * 28 + 38.0 * 15 + 23.1 * 45 + 45.12 * 90
6155.299999999999

Answer 2

My preference is to use a vectorised approach via numpy :

import numpy as np

numbers = [(68.9, 2, 24.8),
           (12.4, 28, 21.12),
           (38.0, 15, 90.86),
           (23.1, 45, 15.3),
           (45.12, 90, 12.66)]

a = np.array(numbers)

res = np.dot(a[:, 0], a[:, 1])

# 6155.3

Answer 3

First off, element[1] will give you the second entry of the tuple, indexing for a tuple or list always starts at 0 . Apart from that, you're giving yourself a hard time with your function by converting variables back and forth. Not sure what you are trying to do with this part anyway:

string_1 = ''.join(str(x) for x in first_decimal)
string_2 = ''.join(str(x) for x in integer)

It seems pretty unecessary. Now to give you a solution that is similar to your approach. Basically, we enumerate through every tuple of the list, multiply the first two entries and add them to the total amound:

numbers = [(68.9, 2, 24.8),
       (12.4, 28, 21.12),
       (38.0, 15, 90.86),
       (23.1, 45, 15.3),
       (45.12, 90, 12.66)]


def function(numbers_list):
    total_add = 0
    # Because numbers is a list of tuples, you can just
    # use `len()` to find the number of tuples
    for tuple in range(len(numbers_list)):
        total_add += numbers_list[tuple][0] * numbers_list[tuple][1]
    return total_add

function(numbers)

or simply:

def function(numbers_list):
        total_add = 0
        for tuple in numbers_list:
            total_add += tuple[0] * tuple[1]
        return total_add

which can be further shortened to Joe Iddons answer:
total_add = sum(t[0] * t[1] for t in numbers)