[Python-Dev] Issue10403 - using 'attributes' instead of members in documentation

[Eric Snow]

On Tue, Jun 28, 2011 at 7:20 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> Michael Foord wrote:
>
>> What do you mean by "instances can have methods as instance attributes"?
>> Once you attach a bound method directly to an instance it becomes a slightly
>> different beast I think. (On top of which that is pretty rare behaviour.)
>
>>>> class C:
> ...     def method(self, x):
> ...             return x+1
> ...
>>>> c = C()
>>>> c.method = types.MethodType(lambda self, x: x+101, c)
>>>> c.method(1)
> 102
>
> I don't know how rare it is, but it's a useful trick for customising the
> behaviour of instances.
>
>
> As I see it, there are three dichotomies we sometimes need to make:
>
>
> (1) Instance attributes vs class (shared) attributes.
>
> Broadly speaking, whether the attribute is in instance.__dict__ or
> type(instance).__dict__.
>
> (2) Computed vs non-computed attributes.
>
> Attributes which are computed by __getattr__ or via the descriptor protocol
> (which includes properties) are all computed attributes; everything else is
> non-computed.
>
> (3) Method attributes (methods) vs non-method/data attributes.
>
> Broadly speaking, methods are callable, non-method (data) attributes are
> not.
>

For terminology, is it important that data attributes are [usually]
not callable, or is it that being callable is not relevant to their
use as attributes of the class/instance?  The same for "methods".

We have precedent for where the the terminology represents an
expectation rather than a firm constraint (__isabstractmethod__).

>
> The three are orthogonal: e.g. a staticmethod is a method by virtue of being
> callable, computed by virtue of being generated by a descriptor, and a class
> attribute by virtue of existing in the type __dict__ rather than the
> instance __dict__.
>
> Strictly speaking, (3) is not truly a dichotomy, since functions and methods
> are first class-objects in Python. E.g. one may store a function as an
> attribute with the intention of using it as data rather than as a method.
> But that's a moderately obscure corner case, and in my opinion it's not
> worth obscuring the practical distinction between "methods are things you
> call, data are not" for the sake of it. Leave the functions-as-data case for
> a footnote.
>

+1

The "three dichotomies" is a great way to look at it.

-eric

>
>
> --
> Steven
>
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