How to add element in Python to the end of list using list.insert?

Question

There is a list, for example,

a=[1,2,3,4]

I can use

a.append(some_value)

to add element at the end of list, and

a.insert(exact_position, some_value)

to insert element on any other position in list but not at the end as

a.insert(-1, 5)

will return [1,2,3,5,4]. So how to add an element to the end of list using list.insert(position, value)?

Solution 1

You'll have to pass the new ordinal position to insert using len in this case:

In [62]:

a=[1,2,3,4]
a.insert(len(a),5)
a
Out[62]:
[1, 2, 3, 4, 5]

Solution 2

list.insert with any index >= len(of_the_list) places the value at the end of list. It behaves like append

Python 3.7.4
>>>lst=[10,20,30]
>>>lst.insert(len(lst), 101)
>>>lst
[10, 20, 30, 101]
>>>lst.insert(len(lst)+50, 202)
>>>lst
[10, 20, 30, 101, 202]

Time complexity, append O(1), insert O(n)

Comments

[David Donari]

Also, using a.insert(-len(a),5) you can insert the element at the beginning lol

[Flux]

If not mistaken, O(n) time complexity for insert is only valid for the average case. Inserting at the end of the list probably has the same cost as appending.

[Kelly Bang]

Or you know, just an a.insert(0, 5) to save you a len lookup

[Lohmar ASHAR]

... this pointed me to the less obvious option ... for my situation ... that is: just use .append :D, might not apply to everyone's situation

[alper]

Does is behave same as append() in the background?