Joining or combining lists in Python is a common operation. Whether you're merging datasets or simply appending items, Python provides multiple ways to join lists efficiently.

1. Using the + Operator

The most straightforward way to join two lists.

Example:

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
combined = list1 + list2
print(combined)

Output:

['a', 'b', 'c', 1, 2, 3]

Creates a new list. Original lists are unchanged.

2. Using extend() Method

Appends all elements of one list to the end of another (modifies the original list).

Example:

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list1.extend(list2)
print(list1)

Output:

['a', 'b', 'c', 1, 2, 3]

Efficient when you want to update the first list directly.

3. Using a Loop (for)

Join lists manually by looping through one and appending to another.

Example:

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
for item in list2:
   list1.append(item)
print(list1)

Output:

['a', 'b', 'c', 1, 2, 3]

Useful when you want custom logic during the merge.

4. Using List Comprehension

Another flexible and Pythonic method to join lists.

Example:

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
combined = [item for item in list1] + [item for item in list2]
print(combined)

Output:

['a', 'b', 'c', 1, 2, 3]

Handy if you want to filter or transform while joining.

5. Using itertools.chain()

For large lists or performance-critical cases, use itertools.

Example:

import itertools
list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
combined = list(itertools.chain(list1, list2))
print(combined)

Output:

['a', 'b', 'c', 1, 2, 3]

 Efficient for joining many iterables at once.

Summary Table