Python list slicing slices the list from start index till end – 1, specified as list elements. So its tricky when we require to also slice the last element of list. Trying to slice till list size + 1 gives an error. Let’s discuss ways in which last element can be included during a list slice.
Method #1 : Using None During list slicing, giving the desired first index K and specifying ‘None’ as the second argument in slicing works internally as slicing all the elements from K in list till end including it.
Python3
# Python3 code to demonstrate# list slicing from K to end# using None# initializing listtest_list = [5, 6, 2, 3, 9]# printing original listprint ("The original list is : " + str(test_list))# index to begin slicingK = 2# using None# to perform list slicing from K to endres = test_list[K : None]# printing resultprint ("The sliced list is : " + str(res)) |
The original list is : [5, 6, 2, 3, 9] The sliced list is : [2, 3, 9]
Time complexity: O(n), where n is the length of test_list.
Auxiliary space: O(n – K), as new list is created to store the sliced sublist.
Method #2 : Leaving the last element empty Usually, not specifying any element as end element of slicing instructs python to include whole list after K in list. But the main drawback in using this is code readability. Hence above method is preferred more than this.
Python3
# Python3 code to demonstrate# list slicing from K to end# without specifying last element# initializing listtest_list = [5, 6, 2, 3, 9]# printing original listprint ("The original list is : " + str(test_list))# index to begin slicingK = 2# without specifying last element # to perform list slicing from K to endres = test_list[K :]# printing resultprint ("The sliced list is : " + str(res)) |
The original list is : [5, 6, 2, 3, 9] The sliced list is : [2, 3, 9]
Time complexity: O(n), where n is the length of the test_list.
Auxiliary space: O(n – K), as we are creating a new list to store the sliced sublist.
Method #3 : Using itertools
Here is an example of using the islice() function from the itertools module to slice a list from the Kth element to the last element:
Python3
from itertools import islice# Initialize the listtest_list = [5, 6, 2, 3, 9]# Index to begin slicingK = 2# Use islice() to slice the list from the Kth element to the last elementres = list(islice(test_list, K, None))print(res) # [2, 3, 9]#This code is contributed by Edula Vinay Kumar Reddy |
[2, 3, 9]
Time complexity: O(n)
Auxiliary space: O(n)
Method 4: Using a for loop to iterate over the list and append elements to a new list starting from the K index.
Step-by-step approach:
- Initialize an empty list to store the sliced list.
- Initialize a variable ‘i’ to 0.
- Iterate over the original list from index ‘K’ to the end using a for loop.
- Append each element to the empty list initialized in step 1.
- Increment ‘i’ by 1 after each iteration.
- Print the sliced list.
Below is the implementation of the above approach:
Python3
# Python3 code to demonstrate# list slicing from K to end# without specifying last element# initializing listtest_list = [5, 6, 2, 3, 9]# printing original listprint ("The original list is : " + str(test_list))# index to begin slicingK = 2# using for loop to slice list from K to endres = []for i in range(K, len(test_list)): res.append(test_list[i])# printing resultprint ("The sliced list is : " + str(res)) |
The original list is : [5, 6, 2, 3, 9] The sliced list is : [2, 3, 9]
Time complexity: O(n), where ‘n’ is the length of the original list.
Auxiliary space: O(n), as we are creating a new list to store the sliced elements.
Method #5: Using list comprehension
- Initialize the input list and the index K
- Use list comprehension to slice the input list from index K to the end.
- Assign the sliced list to a variable ‘res’.
- Print the sliced list.
Python3
# Python3 code to demonstrate# list slicing from K to end# without specifying last element# initializing listtest_list = [5, 6, 2, 3, 9]# printing original listprint ("The original list is : " + str(test_list))# index to begin slicingK = 2# using list comprehension to slice list from K to endres = [test_list[i] for i in range(K, len(test_list))]# printing resultprint ("The sliced list is : " + str(res)) |
The original list is : [5, 6, 2, 3, 9] The sliced list is : [2, 3, 9]
Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), as we are creating a new list to store the sliced element
Method #6: Using numpy:
Algorithm:
- Initialize the list.
- Initialize the starting index to slice from.
- Create a numpy array from the list slicing from the starting index to the end.
- Convert the numpy array back to a list.
- Print the sliced list.
Python3
import numpy as np# initializing listtest_list = [5, 6, 2, 3, 9]# printing original listprint("The original list is:", test_list)# index to begin slicingK = 2# using numpy to slice list from K to endres = np.array(test_list[K:])# printing resultprint("The sliced list is:", res.tolist()) |
Output:
The original list is: [5, 6, 2, 3, 9] The sliced list is: [2, 3, 9]
Time Complexity: The time complexity of the code is O(n), where n is the number of elements in the list. This is because we are creating a numpy array from the list which takes O(n) time, and then converting the numpy array back to a list which also takes O(n) time. All other operations are constant time.
Space Complexity: The space complexity of the code is O(n), where n is the number of elements in the list. This is because we are creating a numpy array from the list which takes O(n) space, and then converting the numpy array back to a list which also takes O(n) space. All other operations are constant space.
