A list is a built-in data type that stores the group of elements under one variable. In this article, we will discuss how to concatenate lists in Python. You will learn how to join two or more lists using various methods.
Here’s a quick summary of all the methods shared in this tutorial.
Python List Concatenation Methods
| Method | Description |
|---|---|
| Concatenation (+) operator | Concatenates elements from two lists into a new list. |
| Extend() method | Extends one list with the elements of another list. |
| Concatenation of two lists using the native method | Iterates over elements of the second list and appends them to the first list. |
| List comprehension | Generates a new list by iterating through existing lists. |
| Concatenate lists using the (*) operator | Unpacks elements and combines them into a new list. |
| itertools.chain() method | Uses itertools.chain() to concatenate lists. |
Let’s now see each of these methods with code examples.
Method 1: Python concatenate lists using the concatenation (+) operator
The Concatenate (+) operator is used between two lists to concatenate elements of multiple lists into a list. Below is the simple code that concatenates multiple items into a new list.
Code:
list1 = ['a', 'b', 'c'] list2 = [1, 2, 3] combined_list = list1 + list2 print(combined_list)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Also Read: How To Find Intersection Of Two Lists In Python
Method 2: Concatenation of Python lists using extend() method
The extend() method is used to concatenate two lists. The extend() method iterates over the passed iterable and adds elements to the list.
Syntax of extend() method: list_1.extend(list_2)
Code:
list1 = ['a', 'b', 'c'] list2 = [1, 2, 3] list1.extend(list2) print(list1)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Method 3: Concatenation of two lists in Python using the native method
In this method, we iterate over the elements of the second list and append those elements one by one into the first list.
Below is an example program that concatenates elements of two lists into a list using a naive method.
Code:
list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
for element in list2:
list1.append(element)
print(list1)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Method 4: Concatenating Python lists using list comprehension
List comprehension generates/builds a list of elements based on existing lists.
An inline for loop is used in the below code to implement the list comprehension to concatenate lists.
Code:
list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
combined_list = [i for j in [list1, list2] for i in j]
print(combined_list)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Method 5: How to concatenate lists in Python using the ‘*’ operator
The ‘*’ operator unpacks the list of elements, and we can use the “*” operator to concatenate the list of elements.
Below is an example program that uses the “*” operator to combine/concatenate lists.
Code:
list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
combined_list = [*list1, *list2]
print(combined_list)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Also Read: Python If Else One Liners Using Ternary Operator
Method 6: Concatenate lists using the itertools.chain() method
The chain() method is present in the itertools module, accepts iterables such as lists, tuples, strings, etc., and returns a sequence of elements.
Before using the chain() method, import the itertools module. Below is the program that uses the itertools.chain() method to concatenate lists.
Code:
import itertools list1 = ['a', 'b', 'c'] list2 = [1, 2, 3] combined_list = list(itertools.chain(list1, list2)) print(combined_list)
Output:
[‘a’, ‘b’, ‘c’, 1, 2, 3]
Summary
Learn the easy steps to concatenate lists in Python. Discover efficient techniques for merging data in this concise guide. Boost your programming skills today with CodeItBro.
Frequently Asked Questions
Q1. Can you concatenate lists in Python?
You can concatenate lists in Python using the “+” operator or the “extend()” method.
For example: list1 + list2 or list1.extend(list2).
Q2. How do you concatenate multiple lists in Python?
Using the (+) operator, extend() method, native method, comprehension, (*) operator, or chain() method.
Q3. What is the fastest way to concatenate lists in Python?
The fastest way to concatenate lists in Python is by using the + operator, which directly combines the lists, providing a quick and efficient solution.
Q4. How do you concatenate string lists in Python?
Yes, in Python, concatenate string lists using the + operator. Example:
list1 = ['hello', 'world'] list2 = ['!', 'Python'] result = list1 + list2.
Q5. How do I merge 3 lists in Python?
To merge three lists in Python, use the + operator: merged_list = list1 + list2 + list3. This concatenates the lists, creating a single merged list.
Q6. How do you merge two lists without duplicates in Python?
To merge two lists without duplicates in Python, use the set function to convert them, then use the union operator. Finally, convert the result back to a list.
Q7. Is concat faster than append?
Yes, concat is generally faster than append for combining strings, as it creates a new string in one step, while append iterates through each element.
Q8. How do I merge two unsorted lists in Python?
Use the extend() method to merge two unsorted lists in Python. Example: list1.extend(list2) combines elements from list2 into list1.
Q9. What is the difference between concat and merge in Python?
Concatenation in Python combines two or more sequences along an axis. Merging combines DataFrames using a common column, aligning rows based on shared values.
Q10. How do I merge two sorted lists recursively?
To merge two sorted lists recursively, compare the first elements. Append the smaller one, then recursively merge the remaining portions until both lists are merged.
