What's New in Python 3.12

Post by ddejohn » Wed, Oct 18, 2023, 6:39 PM UTC

JimDabell wrote: post #58

woolion wrote: post #43

Earlier quoted context omitted.

Of course this only works at one level and not arbitrarily deeply, but you still need to check for None with this code; it may actually be better to write `x.get("key") or {}` so that you always get an empty dict. I write 'may' because the difference between None and an empty dict may be very subtle and rarely does the API specify with enough precision what are supposed to be the semantics of each case.

> x.get("key") or {} This has the side effect of replacing falsy values like False or 0 with an empty dictionary instead of giving you the actual value. For the exact intended behaviour, you do need to explicitly check for None instead of using a short circuit trick with or.

Post by graton » Wed, Oct 18, 2023, 6:43 PM UTC

NoboruWataya wrote: post #34

I suspect people will use these comments to share their wishlist of Python features, so let me add that I really wish Python had a safe navigation operator, for when you are dealing with nested objects that could be None. I have been trying to parse a lot of XML and JSON in Python lately and a feature like that could really help reduce boilerplate checks. https://en.wikipedia.org/wiki/Safe_navigation_operator

    print(jmespath.search(
        expression="some.deep.nested.value",
        data={"some": {"deep": {"nested": {"value": 2}}}},
    ))
    prints 2

    print(jmespath.search(
        expression="some.deep.nested.value2",
        data={"some": {"deep": {"nested": {"value": 2}}}},
    ))
    prints None

Post by o11c » Wed, Oct 18, 2023, 6:47 PM UTC

wodenokoto wrote: post #56

NoboruWataya wrote: post #34

I suspect people will use these comments to share their wishlist of Python features, so let me add that I really wish Python had a safe navigation operator, for when you are dealing with nested objects that could be None. I have been trying to parse a lot of XML and JSON in Python lately and a feature like that could really help reduce boilerplate checks. https://en.wikipedia.org/wiki/Safe_navigation_operator

def safe_navigation(obj, path: List[str], default=None): try: for key in path: obj = obj[key] return obj except KeyError: return default Yeah. I thought it would just be a try-except, but that turned out pretty ugly. But really, how do you know if your path is missing or the object at the end of the path is None, without using exceptions for communicating this?

    def safe_navigation(obj: Any, *path: str, default: Any = None, strict: bool = False) -> Any:
        sentinel = object() if strict else None
        for key in path:
            obj = obj.get(key, sentinel)
            if obj is sentinel:
                return default
        return obj

Post by vitorsr » Wed, Oct 18, 2023, 6:54 PM UTC

Post by dgunay » Wed, Oct 18, 2023, 6:55 PM UTC

spinningslate wrote: post #52

gnulinux wrote: post #11

PEP 695 is great. I've been using mypy every day at work in last couple years or so with very strict parameters (no any type etc) and I have experience writing real life programs with Rust, Agda, and some Haskell before, so I'm familiar with strict type systems. I'm sure many will disagree with me but these are my very honest opinions as a professional who uses Python types every day: * Some types are better than no…

I've been steadily finding the love for F# for sort-of-similar-but-not-quite-the-same reasons. I like Python. It's still my go-to language for most things. But I definitely feel a tail off in utility as code base size increases, and I find myself asking mentally "but what type is that thing?". F# is sort of the opposite of Python. It's strongly, statically and soundly typed, based on Hindley-Milner. It has very good…