append on lists

[Terry Reedy]

Maric Michaud wrote:

> It is, please try to understand it, in python all expressions that mutate an 
> object should return None,

You are over-generalizing.  For builtin classes, mutation methods return 
none.  Guido recommends this as a general practice, but users may do 
whatever they like in their own classes.  In fact, people have been told 
that if they do not like the built-in behavior, they should make their 
own, possibly by subclassing.

For augmented assignment, in-place mutation followed by rebinding is 
explictly allowed and done for lists.

> all expressions that return something, return a new object

Nonesense.  There is nothing in the ref manual that says this and parts 
that say otherwise.

> there are some noticeable exceptions :

They are only exceptions to your rule, not to the language specification.