> On 28 Dec 2020, at 14:00, Inada Naoki <songofaca...@gmail.com> wrote:
>
> On Mon, Dec 28, 2020 at 8:52 PM Phil Thompson
> <p...@riverbankcomputing.com> wrote:
>>
>>
>> I would have thought that an object was defined by its behaviour rather
>> than by any particular implementation detail.
>>
>
> As my understanding, the policy "an object was defined by its
> behavior..." doesn't mean "put unlimited amount of implementation
> behind one concrete type."
> The policy means APIs shouldn't limit input to one concrete type
> without a reason. In other words, duck typing and structural subtyping
> are good.
>
> For example, we can try making io.TextIOWrapper accepts not only
> Unicode objects (including subclass) but any objects implementing some
> protocol.
> We already have __index__ for integers and buffer protocol for
> byts-like objects. That is examples of the policy.
I agree that that would be the cleanest approach, although I worry about
how long it will take until 3th-party code is converted to the new protocol.
That’s
why I wrote earlier that adding this feature to PyUnicode_Type is the most
pragmantic solution ;-)
There are two clear options for a new protocol:
1. Add something similar to __index__ of __fspath__, but for “string-like”
objects
2. Add an extension to the buffer protocol
In either case an ABC for string-like objects would also be nice, to be able
to opt in to the fairly common pattern of excluding strings from types that
can be iterated over, that is:
if isinstance(value, collections.abc.Iterable) and not isinstance(value,
str):
for item in value: proces_item(item)
else:
process_item(value)
Ronald
—
Twitter / micro.blog: @ronaldoussoren
Blog: https://blog.ronaldoussoren.net/ <https://blog.ronaldoussoren.net/>
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