Append at front and remove from rear in Python

When working with Python lists, we often need to add elements to the front and remove elements from the rear. Python provides several efficient methods to accomplish this task, both from the standard library and through built-in operators.

Using + Operator with List Slicing

The simplest approach combines list concatenation with slicing to add an element at the front while removing the last element ?

days = ['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
print("Original list:", days)

# Add 'Mon' at front and remove last element
result = ['Mon'] + days[:-1]
print("After append front and remove rear:", result)

Original list: ['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
After append front and remove rear: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']

Using deque from collections

The deque (double-ended queue) provides efficient operations for adding and removing elements from both ends. This is the preferred method for frequent front/rear operations ?

import collections

days = collections.deque(['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'])
print('Original deque:', days)

# Add element at front and remove from rear
days.appendleft('Mon')
days.pop()

print('After appendleft and pop:', days)

Original deque: deque(['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'])
After appendleft and pop: deque(['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'])

Using insert() and pop() Methods

You can also use list methods directly, though this is less efficient for large lists ?

days = ['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
print("Original list:", days)

# Insert at front (index 0) and remove from rear
days.insert(0, 'Mon')
days.pop()

print("After insert and pop:", days)

Original list: ['Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
After insert and pop: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']

Performance Comparison

Conclusion

Use deque for frequent front/rear operations as it provides O(1) performance. For occasional operations, list slicing with the + operator offers a simple and readable solution.