python - Does insert at the end of a list have O(1) time complexity?

Question

Is there a difference between append and insert at the end of a list? Is insert at the end of a list a constant time operation?

nums = [1, 2, 3]
nums.append(4)  # Time complexity: O(1)
nums.insert(len(nums), 5)  # Time complexity: O(?)

According to the TimeComplexity article in the Python Wiki, the average case for append is O(1), while the average case for insert is O(n). However, in the Python tutorial, it is mentioned that:

... and a.insert(len(a), x) is equivalent to a.append(x).

I'm unsure if "equivalent" there means "equivalent in functionality" or "equivalent in time complexity". Does anyone know?

Answer 1

Worst time complexity for inserting into list is O(n-i), where n is the length of the list and i is the index at which you are inserting.

So in case if you are inserting at the last index, that makes it O(1).

Here is an article that might help you understand better :

https://yourbasic.org/algorithms/time-complexity-arrays/.