trying to getting sum of running list

Question

logic: read list using for loop and add all its elements together and, In end print all the iteration value together in the list

input

lis=[1,1,1,1,1]
ore=[]
for t in lis:
    ore.append(sum(lis[0:lis.index(t)+1]))
    

print(ore)

output

[1, 1, 1, 1, 1]

expected

[1,2,3,4,5]

I have no idea why I am getting output like this one, also want to know about the mechanism of this kind of output. Any possible help is appreciated.

Answer 1

1. The correct way to iterate over both indexes an items with a list is to use enumerate, not to try to find the index after the fact; that’s slow, and fails when the list has duplicate elements (like you found out).

   for i, t in enumerate(lis):
       ore.append(sum(lis[0:i+1]))
   

2. Using sum on a slice that grows by one element each time is also inefficient. You know the sum is only changing by the current value in each iteration, so:

   s = 0
   
   for t in lis:
       s += t
       ore.append(s)
   

Answer 2

Your output is wrong because t represents an item in the lis, not the current index.

Here's the fixed code

lis=[1,1,1,1,1]
ore=[]
for i, t in enumerate(lis):
    ore.append(sum(lis[0:i+1]))

print(ore)

Output:

[1, 2, 3, 4, 5]

Answer 3

you can use np.cumsum() from the numpy library:

import numpy as np
np.cumsum(lis)

returns: a numpy array: [1, 2, 3, 4, 5]