Alternate element summation in list (Python)

Given a list of numbers in this article we are going to calculate the sum of alternate elements in that list.

With list slicing and range

Every second number and also use the range function along with length function to get the number of elements to be summed.

Example

 Live Demo

listA = [13,65,78,13,12,13,65]
# printing original list
print("Given list : " , str(listA))
# With list slicing
res = [sum(listA[i:: 2])
for i in range(len(listA) // (len(listA) // 2))]
   # print result
   print("Sum of alternate elements in the list :\n ",res)

Output

Running the above code gives us the following result −

Given list : [13, 65, 78, 13, 12, 13, 65]
Sum of alternate elements in the list :
[168, 91]

With range and %

Use the percentage operator to separate the numbers at Even and Odd positions. And then add the elements to the respective position of a new empty list. Finally giving a list which shows sum of elements at odd position and sum of elements at even position.

Example

 Live Demo

listA = [13,65,78,13,12,13,65]
# printing original list
print("Given list : " , str(listA))
res = [0, 0]
for i in range(0, len(listA)):
   if(i % 2):
      res[1] += listA[i]
   else :
      res[0] += listA[i]
# print result
print("Sum of alternate elements in the list :\n ",res)

Output

Running the above code gives us the following result −

Given list : [13, 65, 78, 13, 12, 13, 65]
Sum of alternate elements in the list :
[168, 91]