list.insert()

list.insert(i, x)

Returns: None · Updated March 14, 2026 · List Methods

lists methods mutation

The .insert() method adds an element to a list at a specified index. Unlike .append() which always adds to the end, .insert() gives you precise control over where the new element lands. The list is modified in-place and the method returns None.

Syntax

list.insert(i, x)

Parameters

Parameter	Type	Default	Description
`i`	int	—	The index at which to insert the element. Can be positive or negative.
`x`	any	—	The element to insert. Can be of any type.

Examples

Basic usage — insert at the beginning

Insert an element at index 0:

numbers = [1, 2, 3]
numbers.insert(0, 0)
print(numbers)
# [0, 1, 2, 3]

Insert in the middle

Insert an element at a specific position:

letters = ["a", "b", "d", "e"]
letters.insert(2, "c")
print(letters)
# ['a', 'b', 'c', 'd', 'e']

Insert at the end

Using a large index or len() places the element at the end:

fruits = ["apple", "banana"]
fruits.insert(len(fruits), "cherry")
print(fruits)
# ['apple', 'banana', 'cherry']

Negative indices

Negative indices count from the end:

items = [1, 2, 3, 4]
items.insert(-1, "middle")
print(items)
# [1, 2, 3, 'middle', 4]

items.insert(-2, "second-last")
print(items)
# [1, 2, 3, 'second-last', 'middle', 4]

Inserting different types

Python lists are heterogeneous — you can insert any object:

mixed = [1, 2]
mixed.insert(0, "string")
mixed.insert(1, 3.14)
mixed.insert(2, ["a", "list"])
print(mixed)
# ['string', 3.14, ['a', 'list'], 1, 2]

Common Patterns

Building a sorted list incrementally

When you need to maintain sorted order as you add elements:

sorted_nums = [1, 5, 10]
new = 7

import bisect
sorted_nums.insert(bisect.bisect(sorted_nums, new), new)
print(sorted_nums)
# [1, 5, 7, 10]

For frequent sorted insertions, consider using bisect from the standard library.

Inserting at a known position

A common pattern when you know exactly where to insert:

document = ["Paragraph 1", "Paragraph 3"]
document.insert(1, "Paragraph 2")
print(document)
# ['Paragraph 1', 'Paragraph 2', 'Paragraph 3']

Prepending to create a new list

If you need to add multiple elements at the start:

result = [3, 4, 5]
result.insert(0, 2)
result.insert(0, 1)
result.insert(0, 0)
print(result)
# [0, 1, 2, 3, 4, 5]

This is less efficient than concatenating or using a deque for bulk operations.

Inserting None as a sentinel

Sometimes used to mark positions:

data = ["a", "b", "c"]
data.insert(1, None)
print(data)
# ['a', None, 'b', 'c']

Performance Note

Inserting at the end: O(1)
Inserting at the beginning or middle: O(n) — requires shifting elements

For frequent insertions at the beginning, consider using collections.deque:

from collections import deque

dq = deque(["b", "c"])
dq.appendleft("a")
print(list(dq))
# ['a', 'b', 'c']