What's the particular reason that some functions in Python operate "IN PLACE", like [].sort and [].reverse, while some others like [].append not?
2 Answers
According to my Programming Python 4th edition:
By default, pop is equivalent to fetching, and then deleting, the last item at offset −1. With an argument, pop deletes and returns the item at that offset—list.pop(-1) is the same as list.pop(). For in-place change operations like append, insert, del, and pop, no new list is created in memory, so execution is quick (performance may further de- pend upon which end is the “top,” but this in turn depends on Python’s current list implementation, as well as measurement concepts we’ll explore later).
There is actually a whole section devoted to this, but this pretty much answers your question.
Comments
"in-place" refers to a sorting algorithms use of only the memory needed to store the list of items plus some small constant. Append isn't a sorting algorithm and thus "in-place" is not meaningful, or at least wouldn't mean the same thing. You're confusing "in-place" in sorting and whether or not it returns a reference to a new object or a modified version of the same object.
2 Comments
Matt Ball
That's not how "in-place" is used when referring to sorting algorithms, or more generally, algorithms which rearrange arrays/lists.
[].appendnot work "in place" ?appendreturn a new copy of the list, leaving the old one unmodified?[].appendwould obviously just modify the existing data structure, unless it's immutable. en.wikipedia.org/wiki/In-place_sorting.appendbecause the non-in-place version would be calledconcat(and is in fact the+operator).