[Python-ideas] Structural type checking for PEP 484
brenbarn at brenbarn.net
Thu Sep 10 03:50:42 CEST 2015
On 2015-09-09 13:17, Guido van Rossum wrote:
> Jukka wrote up a proposal for structural subtyping. It's pretty good.
> Please discuss.
I'm not totally hip to all the latest typing developments, but I'm not
sure I fully understand the benefit of this protocol concept. At the
beginning it says that classes have to be explicitly marked to support
these protocols. But why is that? Doesn't the existing
__subclasshook__ already allow an ABC to use any criteria it likes to
determine if a given class is considered a subclass? So couldn't ABCs
like the ones we already have inspect the type annotations and decide a
class "counts" as an iterable (or whatever) if it defines the right
methods with the right type hints?
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."
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