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Python – Get sum of last K list items using slice
  • Last Updated : 29 Dec, 2019

Accessing elements in a list has many types and variations. These are an essential part of Python programming and one must have the knowledge to perform the same. This article discusses ways to fetch the last K elements and do its summation. Let’s discuss certain solution to perform this task.

Method #1 : Using list slicing + sum()
This problem can be performed in 1 line rather than using a loop using the list slicing functionality provided by Python and then using sum(). Minus operator specifies slicing to be done from rear end.




# Python3 code to demonstrate 
# Inverse K slice Sum
# using list slicing + sum()
  
# initializing list 
test_list = [4, 5, 2, 6, 7, 8, 10
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# initializing K 
K = 5
  
# Inverse K slice Sum
# using list slicing + sum()
res = sum(test_list[-K:])
  
# print result 
print("The last K elements sum of list is : " + str(res)) 
Output :
The original list : [4, 5, 2, 6, 7, 8, 10]
The last K elements sum of list is : 33

 

Method #2 : Using islice() + reversed() + sum()
The inbuilt funtions can also be used to perform this particular task. The islice function can be used to get the sliced list and reversed function is used to get the elements from rear end and then sum() can be employed to perform summation.






# Python3 code to demonstrate 
# Inverse K slice Sum
# using islice() + reversed() + sum()
from itertools import islice 
  
# initializing list 
test_list = [4, 5, 2, 6, 7, 8, 10
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# initializing K 
K = 5
  
# using islice() + reversed() + sum()
# Inverse K slice Sum
res = list(islice(reversed(test_list), 0, K)) 
res.reverse()
res = sum(res)
  
# print result 
print("The last K elements sum of list are : " + str(res)) 
Output :
The original list : [4, 5, 2, 6, 7, 8, 10]
The last K elements sum of list is : 33

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