Python | Get Last N Elements from Given List

This article discusses ways to fetch the last N elements of a list in Python.

Example: Using list Slicing

test_list = [4, 5, 2, 6, 7, 8, 10]

# initializing N
N = 5

# using list slicing
res = test_list[-N:]

print(str(res))

[2, 6, 7, 8, 10]

Explaination: This problem can be performed in 1 line rather than using a loop using the list-slicing functionality provided by Python. Minus operator specifies slicing to be done from the rear end.

Let's discuss certain solutions to perform this task.

Get the Last N Elements of a List using islice()

The inbuilt islice() functions 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.

from itertools import islice

# initializing list
test_list = [4, 5, 2, 6, 7, 8, 10]

# initializing N
N = 5

# using islice() + reversed()
# Get last N elements from list
res = list(islice(reversed(test_list), 0, N))
res.reverse()

# print result
print("The last N elements of list are : " + str(res))

The last N elements of list are : [2, 6, 7, 8, 10]

Time Complexity: O(n), where n is the length of the list test_list 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list 

Take Last N Elements using Loop

This code extracts the last N elements from a list. It first reverses the list using slicing ([::-1]), then iterates over the first N elements, appending them to a new list res. Finally, it reverses res to restore the original order and prints the last N elements.

# initializing list
test_list = [4, 5, 2, 6, 7, 8, 10]

# initializing N
N = 5

# Get last N elements from list
x=test_list[::-1]
res=[]
i=0
while(i<N):
    res.append(x[i])
    i+=1
res.reverse()

print("The last N elements of list are : " + str(res))

The last N elements of list are : [2, 6, 7, 8, 10]

Python Last N Elements of List using Generator

You can define a generator function that yields the last N elements of a list.

def get_last_n(lst, n):
    yield lst[len(lst)-n:len(lst)]

# initializing list
test_list = [4, 5, 2, 6, 7, 8, 10]

print("The last N elements of list are : " + str(list(get_last_n(test_list, 5))))

The last N elements of list are : [[2, 6, 7, 8, 10]]

Time Complexity : O(N)
Auxiliary Space : O(1)