Python | Remove trailing empty elements from given list

When working with lists in Python, it's common to encounter lists with extra None elements at the end. These trailing None values can cause issues in our programs . We can remove these trailing None elements using simple methods like slicing, loops, or filter.

Using List Slicing

Slicing is a very efficient and simple way to remove unwanted elements from a list. We can use slicing to remove trailing None elements by selecting only the part of the list that has meaningful values. We reverse the list to find how many trailing None elements there are. Then we slice the original list to remove that many None elements from the end. It’s a fast method because slicing is done in one step.

a = [1, 2, 3, None, None, None]
# Slicing to remove trailing None elements
a = a[:len(a) - len([x for x in a[::-1] if x is not None])]
print(a)  

[1, 2, 3]

Other methods that we can use to remove trailing None elements from a list in Python are:

Using filter()

The filter() function is part of Python’s built-in functions and provides a functional way to process lists. We can use it to filter out None elements from the list, but we need to reverse the list first to remove trailing None elements. Finally, we reverse the list back to keep the original order.

a = [1, 2, 3, None, None, None]
# Using filter to remove None elements and reversing the list again
a = list(filter(lambda x: x is not None, a[::-1]))[::-1]
print(a)  

[1, 2, 3]

Using while Loop with del

In addition to using pop(), we can also use the del statement to remove trailing None elements. This method gives us more control over deleting specific elements by their index. The process is similar to the loop with pop(), but instead of removing elements one by one using pop(), we directly delete the last element using del.

a = [1, 2, 3, None, None, None]
# Using del to remove None elements from the end
while a and a[-1] is None:
    del a[-1]
print(a)  

[1, 2, 3]

Using Loop

A simple loop can also be used to remove trailing None elements. This method is easy to understand and works well when you want to remove elements one by one. We check if the last element in the list is None. If it is, we remove it. We repeat this process until the last element is no longer None.

a = [1, 2, 3, None, None, None]
# Loop through the list and remove None elements from the end
while a and a[-1] is None:
    a.pop()
print(a)  

[1, 2, 3]