String summing

Question

So I understand that if you code,
print(sum([1,2,3,4,5])

The result is 15.

Is there a way to just sum the even indexes?

Answer 1

my_list = [1,2,3,4,5]
print(sum(i for i in my_list if not my_list.index(i) % 2))

Answer 2

Brian R definitely not the only way, this is just the most classic way
Quan Nguyen you can use list slicing:

L = [1, 2, 3, 4, 5] # or ant list you want
s = sum(L[::2])

NOTE: There is always a way to do anything, you just have to think :)

Answer 3

I think the only way you can sum the even indexes is by iterating through the list manually. Here's an example:

my_list = [1, 2, 3, 4, 5]
sum = 0
for i in range(len(my_list))
if i % 2 == 0:
sum += my_list[i]

print(sum)

Answer 4

Brian R glad to see people like you trying to help as well!

Answer 5

Oops—totally forgot it could be done like that. Thanks for correcting me!

Answer 6

thanks fellow coders! gives me some insight. I was just wondering if there was some sort of extra coding in the pre built in functions!

Answer 7

Quan Nguyen you can always check for the source code to see what other parameters can be used as well. Anyway, here it is, without the source code:
https://www.google.com/amp/s/www.geeksforgeeks.org/sum-function-JUMP_LINK__&&__python__&&__JUMP_LINK/amp/

Answer: no there isn't

Answer 8

ah that’s what I was looking for!
its sum(a, start)

Answer 9

Quan Nguyen no, this only specifes the start, nothing related to even indexes (except in the case of patterns)

Answer 10

so i think how that works is it will sum string a, and if i put 2 in start it will sum all the second variables?

Answer 11

Quan Nguyen it will start from the third, rememeber, indexes start from 0 not 1. And no, it will sum the variables from index 2 to the end of list

Answer 12

oh got it

Answer 13

Thanks everyone! Thanks David Ashton! I think I liked your solution the best!

Answer 14

L=(1,2,3,4,5,6,7,8,9)
m=round(len(L)/2)
n=L[:m]
print(sum(L)-2*sum(n))