How to Prepend to List in Python
This tutorial covers how to prepend elements to a
list in Python.
Prepend to List in Python using list.insert()
The easiest way to prepend an element to a
list is to use the built-in Python
insert() method. Pass the
list before the method and specify the index as the first argument and the value of the element as the second. Here is an example:
items = [2, 3, 4] items.insert(0, 1) print(items)
[1, 2, 3, 4]
To insert at the beginning of any list we use
0 as that is where the index starts.
What's nice about
inset() is that it can be used to prepend elements to a
list by counting the length of the list to determine the next index like this:
items = [2, 3, 4] items.insert(len(items) -1, 1) print(items)
[2, 3, 4, 1]
Prepend to a Python List Using collections.deque.appendleft()
Another way to prepend to lists in Python is to use the
.deque.appendleft() method from the collections package.
from collections import deque items = [2, 3, 4] res = deque(items) res.appendleft(1) print(list(res))
[1, 2, 3, 4]
The advantage of using this function is it can perform prepend operations faster. On the other hand, it's a bit more clunky to implement and you have to load another package into your program.