Python Standard Library changes in recent years

Re:Python Standard Library changes in recent years by ssl232 on Saturday May 21, 2022 @04:29AM (#31456238)

TIL about dict reverse mapping in 3.10. This will be rather useful:

    people = {
        "Diane": 70,
        "Bob": 78,
        "Emma": 84
    }

    keys = people.keys()
    # dict_keys(['Diane', 'Bob', 'Emma'])

    keys.mapping["Bob"]
    # 78

EDIT: I actually misunderstood this; see comments. The keys.mapping field does not point to the original dictionary. I guess this is actually just about consistency with the way other mappings work? Not so useful (to me) after all.

[ Parent | on HN ]

Re:Python Standard Library changes in recent years by dxdm on Saturday May 21, 2022 @04:47AM (#31456320)

Why would you want a collection of keys to behave like the mapping they came from? Why not pass around the dict itself, when you need access to the values? This seems like it extends the responsibilities of "keys" beyond what they should care about, and the mental overhead grows with it.

Or is this about read-only access? There are better, more explicit ways to accomplish that.

[ Parent | on HN ]

Re:Python Standard Library changes in recent years by matjet on Saturday May 21, 2022 @04:44AM (#31456309)

I do not see the use for this, over the standard access methods.

    people = {
        "Diane": 70,
        "Bob": 78,
        "Emma": 84
    }

    people.get("Bob")
    # 78

The common usecase is:

    for key in people.keys():
        people.get(key)

    keys = people.keys()
    # dict_keys(['Diane', 'Bob', 'Emma'])

    for key in keys:
        keys.mapping[key]

What is the advantage?

[ Parent | on HN ]

Re:Python Standard Library changes in recent years by ssl232 on Saturday May 21, 2022 @04:47AM (#31456325)

It gives you access to the original dictionary from a view. I've not played with it yet but I guess that means you can modify it.

EDIT: apparently not:

    >>> keys.mapping
    mappingproxy({'Diane': 70, 'Bob': 78, 'Emma': 84})

In this case I actually don't know what the use case is :shrug:

[ Parent | on HN ]

Re:Python Standard Library changes in recent years by mjw1007 on Saturday May 21, 2022 @05:14AM (#31456435)

The rationale was here.

https://github.com/python/cpython/issues/85067#issuecomment-...

It seems a bit vague: « Exposing this attribute would help with introspection, making it possible to write efficient functions that operate on dict views. »

[ Parent | on HN ]

Re:Python Standard Library changes in recent years by aidos on Saturday May 21, 2022 @04:47AM (#31456318)

I don’t quite get the usecase for it. You’ve got the original dictionary that gives you exactly the same thing. There’s obviously something I’m not thinking of here but I’m not sure why I would want to trade the dictionary for a set of keys, that’s also the dictionary.

[ Parent | on HN ]