Python - Truncate a list

We are given a list we need to truncate list. For example, we are having a list a = [1, 2, 3, 4, 5] we need to truncate (removing 2 elements from behind) list so that the output should be [1,2,3].

Using List Slicing

List slicing allows truncating a list by specifying the starting and ending indices.

a = [1, 2, 3, 4, 5]
a = a[:3]  # Keeps only the first 3 elements
print(a)  

[1, 2, 3]

Explanation:

• Slicing operation a[:3] creates a new list with the first 3 elements of the original list a.
• List a is then reassigned to this truncated version, resulting in [1, 2, 3], which is printed.

Using del

We can use del to delete specific elements from the list by index or even to remove a range of elements.

a = [1, 2, 3, 4, 5]
del a[-2:]  # Remove the last 2 elements
print(a)  

[1, 2, 3]

Explanation:

• Statement del a[-2:] removes the last two elements from the list a by slicing the list from the second-to-last element to end.
• After the deletion modified list a is printed showing [1, 2, 3]

Using pop()

pop() method removes and returns an element at a specified index from a list. If no index is specified it removes and returns the last element of list.

a = [1, 2, 3, 4, 5]
a.pop()  # Removes last element (5)
a.pop()  # Removes second last element (4)
print(a)  

[1, 2, 3]

Explanation:

• First a.pop() removes last element (5) from list and list becomes [1, 2, 3, 4].
• Second a.pop() removes new last element (4) and final list is [1, 2, 3] which is printed.

Using list

We can truncate a list by directly slicing it or removing elements with methods like del or pop(). Both approaches allow you to shorten the list by removing one or more elements from end or specific positions.

a = [1, 2, 3, 4, 5]
a = a[:len(a) - 2]  # Keep everything except the last 2 elements
print(a) 

[1, 2, 3]

Explanation:

• Expression a[:len(a) - 2] slices the list a, keeping all elements except the last two by calculating new length as len(a) - 2.
• After this operation the list a becomes [1, 2, 3].