On Tue, Oct 19, 2021 at 9:39 AM Chris Angelico <ros...@gmail.com> wrote:
> On Wed, Oct 20, 2021 at 3:25 AM Baptiste Carvello
> <devel2...@baptiste-carvello.net> wrote:
> >
> > Le 18/10/2021 à 20:26, Guido van Rossum a écrit :
> > >
> > > y = None # Default
> > > if config is not None:
> > > handler = config.get("handler")
> > > if handler is not None:
> > > parameters = handler.get("parameters")
> > > if parameters is not None:
> > > y = parameters.get("y")
> > >
> > > […]
> > > Using ?. this can be written as
> > >
> > > y = config?.get("handler")?.get("parameters")?.get("y")
> >
> > Sure, but the EAFP version is not that bad:
> >
> > try:
> > y = config["handler"]["parameters"]["y"]
> > except KeyError:
> > y = None
> >
> > which could be further simplified with an exception-catching expression
> > (caveat: keyword usage is pure improvisation, it sounds good, but is
> > probably broken :-) :
> >
> > y = config["handler"]["parameters"]["y"] with KeyError as None
> >
> > The PEP authors would probably reject this as "hiding errors in code",
> > which is true, but none-aware operators also hide errors…
>
> PEP 463 would like to say hi :)
>
In case it saves anyone a couple clicks:
https://www.python.org/dev/peps/pep-0463/
I also prefer more syntactic help with exceptions, rather than more syntax
emphasizing None's uniqueness.
None and its ilk often conflate too many qualities. For example, is it
missing because it doesn't exist, it never existed, or because we never
received a value, despite knowing it must exist? The languages SAS and R
support at least 27 varieties of NA, allowing un-tagged, and tagged with
the letters A-Z to help someone create distinctions between different kinds
of nothingness. IEEE-754 allows about 16 million possible NaNs, which I
believe was intended to allow floating point instructions to pass error
messages along.
If the motivation for this operator is chained lookups, how about adding a
feature to the operator module, first? It seems natural to add a
keyword-only argument to `attrgetter`, and it's a lighter touch than
implementing a new operator. If use becomes widespread, that gives more
weight to PEP 505.
def attrgetter(*attrs, none_aware=False)
https://docs.python.org/3/library/operator.html#operator.attrgetter
Apologies if attrgetter has already been discussed. I didn't see mention of
it in PEP 505.
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