Sean Sean - 6 days ago 4
Python Question

Function That Computes Sum of Squares of Numbers in List

I'm trying to write a function sum_of_squares(xs) that computes the sum of the squares of the numbers in the list xs. For example, sum_of_squares([2, 3, 4]) should return 4+9+16 which is 29:

Here's what I tried:

import random

xs = []

#create three random numbers between 0 and 50

for i in range(3):
xs.append(random.randint(0,50))

def sum_of_squares(xs):

#square the numbers in the list

squared = i ** i

#add together the squared numbers

sum_of_squares = squared + squared + squared

return sum_of_squares

print (sum_of_squares(xs))


Right now this always prints

12


Because it's taking i as in the number of integers in the list as opposed to the value of the integer. How do I say "multiply the value by the value of the integer" for as many integers are in the list to get the squared values?

Asking that question led me to try this:

import random

xs = []

#create three random numbers between 0 and 50

for i in range(3):
xs.append(random.randint(0,50))

def sum_of_squares(xs):

#square the numbers in the list

for i in (xs):
squared = i ** i

#add together the squared numbers

sum_of_squares = squared + squared + squared

return sum_of_squares

print (sum_of_squares(xs))


But it doesn't seem to be squaring the values of the integers correctly - I'm not sure what it's doing. See this screenshot See Screenshot of a Visualize Python walkthrough.

Answer

you are doing silly mistakes. try this:

import random
xs = []
for i in range(3):
    xs.append(random.randint(0,50))

def sum_of_squares(xs):
    sum_of_squares=0  #mistake 1 : initialize sum first. you are making new sum variable in loop everytime. 
    for i in (xs):
        squared = i * i  #mistake 2 : ** is exponent and not multiply.
        sum_of_squares += squared  #mistake 3
    return sum_of_squares

print (sum_of_squares(xs))