Question

What’s the particular reason that some functions in Python operate “IN PLACE”, like [].sort and [].reverse, while some others like [].append not?

Answer 1

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.