Which is costlier? Mutating object or creating new object?

Asked Aug 21 '19 at 15:12

Active Aug 21 '19 at 15:28

Viewed 41 times

Consider I have two lists in python a = [1, 2, 3] and b = [4, 5]. I want to concatenate these two lists and it doesn't matter if the existing object changes.

As far as I know, we can do this in two ways as follow

a.extend(b), here a will have the concatenated result i.e [1, 2, 3, 4, 5]

c = a + b, c will have the same result.

I know that the first one mutating the same object while the second creates a new object. But which one is more costlier in terms of performance? Which method is advisable?

edited Aug 21 '19 at 15:28

asked Aug 21 '19 at 15:12

Manoj Kumar S

4

see this solution for a small benchmark https://stackoverflow.com/a/56407963/6260170 – Chris_Rands Aug 21 '19 at 15:18
in practical terms this is definitely a mico-optimisation that you should not worry about – Chris_Rands Aug 21 '19 at 15:19
`a.extend(b)` makes you think about the state of `a` at different times. `a + b` discards the value. Perhaps you want `c = a + b`? – Caleth Aug 21 '19 at 15:22
Yes you are right. it is `c = a + b`. Updated the question. – Manoj Kumar S Aug 21 '19 at 15:29
2

Well, not exactly a duplicate of the proposed (as OP clearly knows how to concat lists), but the attached answer definitely answers this... – Tomerikoo Aug 21 '19 at 15:37

Which is costlier? Mutating object or creating new object?

0 Answers0