python program to print sum of consecutive numbers in a range

Question

write a python program to print sum of 3 consecutive numbers in a range in a list. for example we take input n = 8 so the program will print [1+2+3,2+3+4,3+4+5,4+5+6+,5+6+7,6+7+8] means the output should be =[6,9,12,15,18,21] i am new in programming, my code is:-

arr=[]
N=int(input("enter the value of N"))
def lst(arr):
    for i in range(N):
        x=[i]+[i+1]+[i+2]
        arr.append(x)
lst(arr)
print(arr)

Answer 1

This will give you the output you are looking for. It starts indexed at 1 instead of 0 and calls sum on the lists you are creating in each iteration.

Edit: as pointed out in the comments, creating these lists is unnecessary you can just do a sum.

arr=[] 
N=int(input("enter the value of N")) 
def lst(arr): 
    for i in range(1, N - 1): 
        x = (i) + (i + 1) + (i + 2) # for ease of reading 
        arr.append(x) 
        

lst(arr) 
print(arr)

Answer 2

Using list comprehension - given a list and a length of interest lgt:

l = list(range(1, 9))
lgt = 3

print([sum(l[i-lgt:i]) for i in range(lgt, len(l) + 1)])

OUTPUT

[6, 9, 12, 15, 18, 21]

Answer 3

Why can't you use list comprehension,

In [1]: [(i+1) + (i+2) + (i+3) for i in range(7)]
Out[1]: [6, 9, 12, 15, 18, 21, 24]