Python List insert() Method

Q: How do I add an element at the beginning of a list in Python?

Use `my_list.insert(0, item)`. For very large lists that you change at the front often, a `collections.deque` with `appendleft()` is faster.

Q: What is the difference between insert() and append()?

`append()` always adds at the end, while `insert()` adds at any index you choose and moves the later items to the right.

By Yogesh Sharma (LinkedIn) · Every code example is run and checked on Python 3.13 (how we test) · Last updated 21 Oct 2026

Short answer

list.insert(index, item) puts item before the position index, shifts the later items one place to the right, changes the list in place and returns None.

While append() always adds at the end, insert() lets you choose where the new item goes. Use it to put a value at the front of a queue, to keep a short list in a particular order or to place a header before the data.

The index works like the index you use in slicing: 0 is the first position and negative numbers count from the end. Unlike reading with my_list[i], insert() never raises an IndexError for an index that is too large or too small.

Quick facts
Syntax	`my_list.insert(index, item)`
Parameters	`index`: position to insert before; `item`: the object to insert
Returns	`None` (the list is modified in place)
Time complexity	O(n), because later items must shift

How list.insert() chooses the position

The new item ends up at index, and the item that used to be there moves right together with everything after it. So insert(0, x) places x first and insert(1, x) places it second.

Python

letters = ["a", "c", "d"]
letters.insert(1, "b")
print(letters)
letters.insert(0, "start")
print(letters)

Negative and out-of-range indexes in insert()

A negative index counts from the end, but remember that the item goes before that position. So insert(-1, x) places x just before the last item, not after it. An index larger than the length simply appends the item at the end, and a very negative index inserts at the front. No error is raised in either case.

Call on [10, 20, 30]	Result
`insert(0, 5)`	`[5, 10, 20, 30]`
`insert(2, 25)`	`[10, 20, 25, 30]`
`insert(-1, 25)`	`[10, 20, 25, 30]`
`insert(99, 40)`	`[10, 20, 30, 40]`
`insert(-99, 0)`	`[0, 10, 20, 30]`

insert() performance and better choices for queues

Inserting near the front is slow for long lists, because Python has to move every following item. For a handful of items that does not matter. If you repeatedly add to or remove from the front of a large collection, use collections.deque, which handles both ends in constant time. To add several items at a position at once, assign to a slice such as items[1:1] = ["x", "y"]. For plain additions at the end, append() and extend() are the right tools.

Examples you can run

Press Run, then edit the code and run it again.

Insert at the front and in the middle

Add a student to a roll call list at two different positions.

Insert at the front and in the middle

roll = ["Asha", "Dev", "Meera"]
roll.insert(0, "Zoya")
roll.insert(2, "Ravi")
print(roll)

Expected output['Zoya', 'Asha', 'Ravi', 'Dev', 'Meera']

Index larger than the list

An index past the end does not fail; the item is added last.

Index larger than the list

cart = ["pen", "book"]
cart.insert(10, "lamp")
print(cart)
cart.insert(-1, "mug")
print(cart)

Expected output['pen', 'book', 'lamp']
['pen', 'book', 'mug', 'lamp']

Keep a list sorted while inserting

Find the right position with a loop, then insert there.

Keep a list sorted while inserting

scores = [55, 70, 90]
new = 80
pos = 0
while pos < len(scores) and scores[pos] < new:
    pos += 1
scores.insert(pos, new)
print(scores)

Expected output[55, 70, 80, 90]

Common mistakes

Swapping the arguments

✗ Wrong

tasks = ["read", "write"]
tasks.insert("plan", 0)

TypeError: 'str' object cannot be interpreted as an integer

✓ Right

tasks = ["read", "write"]
tasks.insert(0, "plan")
print(tasks)

The index comes first, then the item: insert(0, "plan").

Expecting insert(-1, x) to add at the end

✗ Wrong

nums = [1, 2, 3]
nums.insert(-1, 99)
print(nums)

[1, 2, 99, 3] (not at the end)

✓ Right

nums = [1, 2, 3]
nums.append(99)
print(nums)

The item goes before the position. To add at the very end use append(99) or insert(len(nums), 99).

Using the return value

✗ Wrong

a = [1, 3]
a = a.insert(1, 2)
print(a)

None

✓ Right

a = [1, 3]
a.insert(1, 2)
print(a)

insert() returns None; call it on its own line.

Python List insert() Method: questions people ask

How do I add an element at the beginning of a list in Python?

Use my_list.insert(0, item). For very large lists that you change at the front often, a collections.deque with appendleft() is faster.

What happens if the index in insert() is out of range?

Nothing bad: Python does not raise an error. An index past the end appends the item, and a very negative index inserts it at the front.

What is the difference between insert() and append()?

append() always adds at the end, while insert() adds at any index you choose and moves the later items to the right.

Keep learning

Step-by-step lessons:
Python Lists Python List Methods Python Slicing

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