Suggestion: make sequence and map interfaces more similar

[Antoon Pardon]

Op 30-03-16 om 07:43 schreef Steven D'Aprano:
> Yes, we're all very impressed that you spotted the trivial and obvious 
> loophole that changing a key:value will change the key:value that you just 
> changed *wink* but that doesn't really move the discussion anywhere.
>
> 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.
>
> Given a surjection (many-to-one mapping) between keys and values in a 
> mapping, we expect that changing the mapping of one key will not affect 
> other keys. To be pedantic, by "change" I mean deleting the key (and, if 
> necessary, value) or reassigning a new value to the key. To be even more 
> pedantic, mutations to the value *do not count*.

I don't expect that generally. Sure there are specific mapping implementations
for which this is true, but I see no reason to limit the word mapping only to
those kind of data-types.

What I want from a mapping is that it gives me the correct correspondence between
a key and a value for the application I am using it for. If that means a "stable"
mapping I'll limit the operations on that mapping as to keep it that way. Which
in a number of case can be perfectly done with python-lists.

So generally there is no reason to limit the word "mapping" to stable mappings.

-- 
Antoon Pardon