dunder-docs (was Python is DOOMED! Again!)

[Devin Jeanpierre]

On Mon, Feb 2, 2015 at 4:06 AM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
>> On Sun, Feb 1, 2015 at 11:15 PM, Steven D'Aprano
>> <steve+comp.lang.python at pearwood.info> wrote:
> Both K.f and K.g are methods, even though only one meets the definition
> given in the glossary. The glossary is wrong.

I agree, it oversimplified and has made a useless distinction here.

>>> Even if it is so defined, the definition is wrong. You can define methods
>>> on an instance. I showed an example of an instance with its own personal
>>> __dir__ method, and showed that dir() ignores it if the instance belongs
>>> to a new-style class but uses it if it is an old-style class.
>>
>> You didn't define a method, you defined a callable attribute.
>
> That is wrong. I defined a method:
>
> py> from types import MethodType
> py> type(instance.f) is MethodType
> True
>
>
> instance.f is a method by the glossary definition. Its type is identical to
> types.MethodType, which is what I used to create a method by hand.

You are assuming that they are both methods, just because they are
instances of a type called "MethodType". This is like assuming that a
Tree() object is made out of wood.

The documentation is free to define things in terms other than types
and be correct. There are many properties of functions-on-classes that
callable instance attributes that are instances of MethodType do not
have, as we've already noticed. isinstance can say one thing, and the
documentation another, and both can be right, because they are saying
different things.


For an example we can all agree on, this is not an instance of
collections.Iterable, but the docs claim it is iterable:
https://docs.python.org/2/glossary.html#term-iterable

    class MyIterable(object):
        def __getitem__(self, i): return i

The docs are not "wrong", they are just making a distinction for
humans that is separate from the python types involved. This is OK.

-- Devin