Suggestion: make sequence and map interfaces more similar

[Random832]

On Wed, Mar 30, 2016, at 01:43, Steven D'Aprano wrote:
> This is not an argument about dicts being mutable, because clearly they 
> aren't. This is an argument about key:value pairs being stable. "Stable" 
> doesn't mean "immutable". If you change the value associated with a key 
> directly, then it will change. That's the whole point. But if you change 
> *one* key, the relationship between *other* keys and their values
> shouldn't 
> change.

This doesn't mean that an object violates the contract by having a
method that changes the relationships between multiple keys and values.
I had considered including an example of replacing the _whole
dictionary_ with a new object in the ellipsis.

Absolutely nothing is stable under a *completely unrestricted* set of
operations.

> Specifically, insertions and deletions to the mapping never affect the 
> existing keys.

You can't say that, because there is no insert and delete method in the
mapping interface.

> If somebody wants to insist that this is a kind of mapping, I can't 
> disagree, but it isn't useful as a mapping type.

Javascript seems to manage it just fine.