How to Join Lists in Python

Python gives you several ways to combine lists and to turn a list of strings into a single string. This page covers both tasks clearly:

• Joining lists — merging two or more lists into one new list (using +, extend(), unpacking, or itertools.chain).
• Joining list elements into a string — using the str.join() method, which concatenates the items of a list into a delimited string.

Understanding the difference between these two operations prevents a common source of confusion for beginners.

Joining Two Lists into One

Using the + Operator

The simplest way to merge two lists is the + operator. It returns a new list containing all elements from both operands without changing the originals.

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = list1 + list2
print(combined)

Output:

[1, 2, 3, 4, 5, 6]

You can chain + to merge more than two lists in one expression: a + b + c.

Using the extend() Method

extend() appends all elements of one list to the end of another in place. Unlike +, it modifies the original list and does not create a new one.

list1 = [1, 2, 3]
list2 = [4, 5, 6]
list1.extend(list2)
print(list1)

Output:

[1, 2, 3, 4, 5, 6]

Use extend() when you do not need to keep the original list1 intact and want to avoid creating an extra copy in memory.

extend() vs append(): append() adds its argument as a single element, so list1.append(list2) produces [1, 2, 3, [4, 5, 6]] — a nested list, not a merged one. Always use extend() when you want to flatten the second list into the first.

Using Unpacking (* Operator)

Python 3.5 and later allow the starred unpacking syntax inside a list literal. This is concise and works with any number of iterables in a single expression.

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = [*list1, *list2]
print(combined)

Output:

[1, 2, 3, 4, 5, 6]

You can also insert extra elements inline: [0, *list1, *list2, 7].

Using itertools.chain()

itertools.chain() from the standard library joins any number of iterables lazily — no intermediate list is created until you request the values. This is the most memory-efficient option when you are processing large sequences.

import itertools

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = list(itertools.chain(list1, list2))
print(combined)

Output:

[1, 2, 3, 4, 5, 6]

Pass itertools.chain(*nested) to flatten a list of lists in one call.

Joining List Elements into a String with str.join()

str.join() is a string method — it is called on the delimiter string and takes an iterable as its argument. It returns a single string with all elements concatenated, separated by the delimiter.

delimiter.join(iterable)

Basic Example

Output:

apple, banana, cherry

Pass an empty string '' as the delimiter to concatenate with no separator at all.

Common Delimiters

Joining a List of Numbers

str.join() requires every element to be a string. Passing integers directly raises a TypeError. Convert them first with map(str, ...) or a generator expression.

nums = [10, 20, 30]
result = ', '.join(map(str, nums))
print(result)

Output:

10, 20, 30

Using a generator expression achieves the same result and lets you format each number as you go:

Output:

12345

Building Multi-line Strings

'\n'.join() is the idiomatic way to build a multi-line string from a list of lines without trailing newlines.

lines = ['line one', 'line two', 'line three']
block = '\n'.join(lines)
print(block)

Output:

line one
line two
line three

Choosing the Right Approach

Related Topics

• Python Lists — creating, indexing, and slicing lists
• List Methods — full reference for append(), extend(), remove(), and more
• Loop Lists — iterating over list elements with for and while
• Copy Lists — shallow vs deep copying
• List Comprehension — building and transforming lists in one expression
• Concatenate Strings — other ways to build strings from parts

Practice