# Write a program to form a cumulative sum list in Python

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The cumulative sum till ith element refers to the total sum from 0th to ith element.

The program statement is to form a new list from a given list. The ith element in the new list will be the cumulative sum from 0 to ith element in the given list.

For example,

### Input

[10,20,30,40,50]

### Output

[10,30,60,100,150]

### Input

[1,2,3,4,5]

### Output

[1,3,6,10,15]

Following is a program to form a cumulative sum list using the input list −

• The input list is passed to the function cumSum() which returns the cumulative sum list.

• We declare an empty list cum_list to which we will append elements to form the cumulative sum list.

• Initialize a sum variable sm=0.

• Start iterating over the input list, with each iteration we increment the sum value to previous value+ the current element.

• On each iteration, the sum value is appended to the cum_list.

• Thus, on ith iteration, the sum variable will contain sum till the ith element(included), which is then appended to the cum_list.

• After iterating through the whole list, the cum_list is returned.

## Example

Live Demo

def cumSum(s):
sm=0
cum_list=[]
for i in s:
sm=sm+i
cum_list.append(sm)
return cum_list

a=[10,20,30,40,50]
print(cumSum(a))

## Output

[10, 30, 60, 100, 150]