Merge Two Lists in Python

In Python, there are many ways to join, or concatenate, two or more lists in Python. Check out the article below to learn more about Merge Two Lists in Python.

What is Python Join Two Lists?

Merging a list refers to adding or concatenating one list with another. Also, it refers to adding two lists. The methods that are used to join the Python list are given below:

a. Using the Naive Method

b.Using the + operator

c.Using the list comprehension

d.Using the extend () method

e.Using the * operator

f.Using the itertools.chains

g.Merge two List using reduce

How to Merge two lists in Python using Method

The list comprehension will help to accomplish the task of the list concatenation. Whereas, the new list will be created.

Example

# Method 1: Using extend() method
def merge_lists_method1(list1, list2):
    merged_list = list1.copy()  # Make a copy of list1 to preserve original data
    merged_list.extend(list2)  # Extend the list with elements from list2
    return merged_list

# Method 2: Using + operator
def merge_lists_method2(list1, list2):
    merged_list = list1 + list2  # Concatenate the two lists using the + operator
    return merged_list

# Example lists
list1 = [1, 2, 3]
list2 = [4, 5, 6]

# Output of Method 1
merged_list_method1 = merge_lists_method1(list1, list2)
print("Merged list using extend() method:", merged_list_method1)

# Output of Method 2
merged_list_method2 = merge_lists_method2(list1, list2)
print("Merged list using + operator:", merged_list_method2)

Output

Merged list using extend() method: [1, 2, 3, 4, 5, 6]
Merged list using + operator: [1, 2, 3, 4, 5, 6]

How to Merge two lists using the extend()

The extend() is a function that allows you to extend by list in Python and then perform the task. So, this function will do the in-place extension of the first list.

Example

def merge_lists(list1, list2):
    merged_list = list1.copy()  # Make a copy of list1 to preserve original data
    merged_list.extend(list2)  # Extend the list with elements from list2
    return merged_list

# Example lists
list1 = [1, 2, 3]
list2 = [4, 5, 6]

# Merge the lists using extend() method
merged_list = merge_lists(list1, list2)

# Output the merged list
print("Merged list using extend() method:", merged_list)

Output

Merged list using extend() method: [1, 2, 3, 4, 5, 6]

How to Join Two Lists Using * Operator in Python?

This method will be performed with the help of the * operator. It is the new addition to the list concatenation and will work only in Python 3.6+. So, any no of the list will be concatenated and returned to the new list using the operator.

Example

def join_lists(list1, list2):
    joined_list = [*list1, *list2]  # Concatenate the two lists using the * operator
    return joined_list

# Example lists
list1 = [1, 2, 3]
list2 = [4, 5, 6]

# Join the lists using * operator
joined_list = join_lists(list1, list2)

# Output the joined list
print("Joined list using * operator:", joined_list)

Output

Joined list using * operator: [1, 2, 3, 4, 5, 6]

How to join two lists using the itertools. chain() in Python?

itertools.chain() is a function in Python that combines multiple lists into a single iterable (something you can iterate over, like a list). Hence, it doesn’t create a new list by combining them, instead, it just gives you a way to access all the elements from all the lists one after the other without storing them in memory.

Example

import itertools

# Define the lists
list1 = [1, 2, 3]
list2 = [4, 5, 6]

# Use itertools.chain() to join the lists
joined_list = itertools.chain(list1, list2)

# Output the joined list
print("Joined list using itertools.chain():", list(joined_list))

Output

Joined list using itertools.chain(): [1, 2, 3, 4, 5, 6]

How to Concatenate two lists using the reduce () function in Python?

First, we import the reduce function from the functools library, which helps us perform operations on lists. Then, we create two lists, list1, and list2, each containing some elements. Next, we combine these lists into a nested list called nested_list. Using the reduce() function, we merge the lists within nested_list.

Within the reduce() function, we use a lambda function, which works similarly to the mini-function used for a single purpose, to concatenate each list in the nested list. Finally, the result of the concatenation is stored in the variable result, which holds the joined list. This joined list is then printed as the final output.

Conclusion

In Python, merging two lists can be achieved using different methods, such as the extend() method, the + operator, and itertools. chain(), or even the reduce() function from the functools library. Each method offers its way of combining lists, catering to different needs and preferences.

Whether you’re simply concatenating lists, chaining their elements together, or reducing them into a single list, Python provides versatile solutions to merge lists efficiently. By understanding these methods, you can choose the one that best fits your specific requirements when working with lists in Python.

Merge Two Lists in Python- FAQs