Haven't noticed an answer to this. Did I miss anything?
On 20/01/19 11:07 AM, Avi Gross wrote:
> Short question. Checking if a protocol is set up?
=do you mean that to check/require that a class exhibits a particular
protocol we should use abstract classes - will not instantiate unless
all the required components are coded?
> Many python improvements are changes to classes that implement a protocol.
> There are things you can do to make your own classes work with the protocol
> by setting various dunder variables like __iter__, __next__ and writing
> appropriate ode including throwing the right error class when done.
> Similarly the "with" statement works with objects that implement __enter__
> and __exit__. There can be plenty of others like this and more can be
> anticipated in the future.
> So, several related questions. Tools that help a developer add appropriate
> things to an object to implement the protocol or to test if it was done
> right. Perhaps a function with a name like is_iterable() that tells if the
> protocol can be applied. For the specific case of an iterable, I found
> something that seems to work for at least some cases:
> from collections import Iterable
> item = [1, 2, 3, 4]
> isinstance(item, Iterable)
> Not sure if it would work on one I created that did the right things or what
> it checks.
=your code should be 'approved' if it implements the next() method, etc.
Did you try such?
> I am interested in a pointer to something that describes many of the known
> protocols or extensions and maybe to modules designed sort of as I said
> above. I am aware some protocols may be not-quite standard with parts of the
> protocol embedded in different objects like wrappers or objects returned
> upon a request to have a proxy and many other techniques that seem to abound
> and allow multiple layers of indirection or seemingly almost magical as in
> multiple inheritance drop-ins and so on. That is what may make these things
> harder if someone uses something like __getattr__ or descriptors to
> intercept calls and provide the functionality without any actual sign of the
> dunder key normally expected.
=Questioning similarly, I recall finding one of these - but do you think
that I can re-find it now? Apologies.
I (too) think it would be handy to have such a list. There are many for
the 'magic methods' themselves, in all the better Py3 texts.
Yesterday I needed to add __LT__() to allow a list of class instances to
be sorted, __EQ__ to enable a list of (other) instances to be searched
(if element in list_of_instances), and made a class callable
(__call__()). Each time I wondered: is this the best way to accomplish
or is there already a mechanism I could be employing/not 'reinventing
the wheel'. (perhaps incompletely!)
For your further reading pleasure (maybe):
On the this topic, one of many references is Interfaces in Python:
Protocols and ABCs
Which reminded me of the amusingly titled: Duck Typing vs. Goose Typing,
Diving into the docs (although not finding exactly what we seek):
- didn't include all, eg context managers:
At a deeper level:
- again, incomplete in the sense (I gained) of this enquiry.
Hopefully there's something to keep your mind occupied...