[Python-ideas] An ABC representing "Iterable, Sized, Container"

Bar Harel bzvi7919 at gmail.com
Mon Jul 25 17:29:08 EDT 2016

Guido, I'm not entirely sure if you're joking or not, but if we'll start
with this, we will never finish.

I believe that although str/bytes truly are special regarding iterables,
the combinations are endless.
Soon enough we'll have NotBytesSequence, NumericSequenceWithoutFloat and

We cannot guarantee a "meaning". We can however guarantee an interface or
API, in this case __iter__,
and promote duck-typing in order to support even the craziest custom

I think breaking the design or the state-of-mind in case of "
IterableButNotString" would be a mistake, unless
we're planning to remove str's __iter__ altogether (which I don't support
either but who knows).

Nevertheless, +1 for the unification of Iterable, Sized and Container or
"Reiterables" as it declares a clearer interface.

On Mon, Jul 25, 2016 at 9:03 PM Guido van Rossum <guido at python.org> wrote:

> On Mon, Jul 25, 2016 at 10:19 AM, Gregory P. Smith <greg at krypto.org>
> wrote:
> > Given how often the str problem comes up in this context, I'm thinking a
> > common special case in type annotation checkers that explicitly exclude
> str
> > from consideration for iteration.  It's behavior is rarely what the
> > programmer intended and more likely to be a bug.
> Should we have IterableButNotString, CollectionExceptString,
> NonStringSequence, or all three? I suppose the runtime check would be
> e.g. isinstance(x, Iterable) and not isinstance(x, (str, bytes,
> bytearray, memoryview))? And the type checker should special-case the
> snot out of it?
> --
> --Guido van Rossum (python.org/~guido)
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