In-place vs. Out-of-place operations

Last Updated: September 1, 2023 9:26 AM UTC

Last edited by:

Daniel Gu <[email protected]>

GitHub <[email protected]>

Improve the `in-place` tag (#2737)

* Rewrite the in-place tag

* Fix typo: extra newline

In programming, there are two types of operations: - "In-place" operations, which modify the original object - "Out-of-place" operations, which returns a new object and leaves the original object unchanged

For example, the .sort() method of lists is in-place, so it modifies the list you call .sort() on:

>>> my_list = [5, 2, 3, 1]
>>> my_list.sort()  # Returns None
>>> my_list
[1, 2, 3, 5]

On the other hand, the sorted() function is out-of-place, so it returns a new list and leaves the original list unchanged:

>>> my_list = [5, 2, 3, 1]
>>> sorted_list = sorted(my_list)
>>> sorted_list
[1, 2, 3, 5]
>>> my_list
[5, 2, 3, 1]

In general, methods of mutable objects tend to be in-place (since it can be expensive to create a new object), whereas operations on immutable objects are always out-of-place (since they cannot be modified).