List concatenation and repetition in Python

Introduction

List concatenation and repetition help you combine lists or repeat their items easily, just like joining or copying groups of things in real life.

When you want to join two lists of groceries into one big list.

When you need to repeat a list of tasks multiple times.

When creating a pattern by repeating a list of colors.

When merging guest lists from two events.

When you want to duplicate a list of default settings.

Syntax

Python

list1 + list2  # Concatenates two lists
list * n       # Repeats the list n times

The + operator joins two lists into a new list without changing the originals.

The * operator repeats the list items n times, creating a new list.

Examples

Concatenates two lists of fruits into one list.

Python

fruits = ['apple', 'banana']
more_fruits = ['orange', 'grape']
all_fruits = fruits + more_fruits
print(all_fruits)

Repeats the list of numbers three times.

Python

numbers = [1, 2, 3]
repeated_numbers = numbers * 3
print(repeated_numbers)

Concatenating an empty list with another list returns the other list.

Python

empty_list = []
result = empty_list + [1, 2]
print(result)

Repeating a list with one item multiple times.

Python

single_item = [5]
repeated_single = single_item * 4
print(repeated_single)

Sample Program

This program shows how to join two lists of fruits and how to repeat a list of numbers multiple times.

Python

fruits = ['apple', 'banana']
more_fruits = ['orange', 'grape']
print('Before concatenation:', fruits)
print('Second list:', more_fruits)
all_fruits = fruits + more_fruits
print('After concatenation:', all_fruits)

numbers = [1, 2, 3]
print('Original numbers:', numbers)
repeated_numbers = numbers * 3
print('After repetition:', repeated_numbers)

Important Notes

Concatenation (+) creates a new list and does not change the original lists.

Repetition (*) also creates a new list; the original list stays the same.

Both operations have time complexity proportional to the size of the resulting list.

Avoid using repetition with very large numbers to prevent memory issues.

Use concatenation when you want to combine lists; use repetition when you want to duplicate list items.

Summary

Use + to join two lists into one bigger list.

Use * to repeat the items in a list multiple times.

Both create new lists and do not change the original lists.