On Fri, Mar 05, 2021 at 04:27:27PM -0000, Vincent Cheong wrote:
> Currently, list.reverse() only works for an entire list. If one wants
> to reverse a section of it 'in-place', one needs to slicing which
> makes the space complexity no longer O(1).
The space complexity of a list is not constant, O(1).
The lists [] and [1]*100000 do not take the same amount of space.
I think that, perhaps, you are trying to say that reversing a list
requires no additional storage and can be done in place.
But having said that, I think that giving `list.reverse()` optional
start and end parameters would probably be a simple and easy change to
make, and would be backwards compatible.
But even easy changes have some cost: the work has to be done, tests
written and run, documentation updated, and that adds one more thing for
people to learn. To balance those costs, we require something more than
"Wouldn't it be good...?", we require an actual, real life use-case for
the feature. (And even then, it's not a guarantee that we will accept
the proposed feature.)
1. What are you doing that you need to reverse just a section of
the list?
2. Is the performance (time or space) of this task so critical
that you can't just use slicing?
mylist[start:end] = mylist[end-1:start-1:-1]
Some additional questions:
- Do we extend this feature to the `reversed()` built-in?
- What about sorting?
--
Steve
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