a=[1,2,3,4].reverse() - why "a" is None?

[Diez B. Roggisch]

Nadav Chernin wrote:

> 
> Chris Withers wrote:
> 
> ...becauase you were looking for:
> 
> reversed([1,2,3,4])
> 
> OK, but my question is generic. Why when I use object's function that
> changed values of the object, I can't to get value of it on the fly
> without writing additional code?
> 
>>>> a=[1,3,2,4]
>>>> a.sort()
>>>> a.reverse()
>>>> a
> [4, 3, 2, 1]
> 
> Why I can't a==[1,3,2,4].sort().reverse() ?

This is a FAQ. The reasoning is that operations that modify a collection in
place (the same goes for .sort()) don't return the collection to prevent
errors from creeping up like this:

  unsorted = ...
  sorted = unsorted.sort()

where the assumption is that unsorted is still that - unsorted.

You can read a lot of the pro + cons on this NG/ML if you google for it, but
you won't reach a change in semantics.

Diez