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newb question about @property


On Mon, Oct 2, 2017 at 5:34 PM, Marko Rauhamaa <marko at pacujo.net> wrote:
> Chris Angelico <rosuav at gmail.com>:
>
>> Yes, that's correct. The *descriptor* protocol is what allows
>> "foo.bar" to cause a function to be executed
>
> That mechanism allows you to expose data fields in the API. If the
> implementation later changes, you can emulate the data fields.
>
> I must say, though, I have yet to run into a need for descriptors.

The beauty of Python (over, say, C++) is that you can transparently
convert something from being a simple data attribute to being a
descriptor. The mere fact that they *exist* benefits your code;
they're like a safety net that lets you do what makes sense without
worrying that someday, maybe, one of these things might have to become
a function. In C++, if something might ever need to be a function, it
has to be a function *now*, so Best Practice is to write getters and
setters for everything, just in case. In Python, you can convert it to
use @property if you ever actually need to, which means you do nothing
now.

>> the *decorator* protocol is what lets you "tag" a function:
>
> i have yet to need that, either. I have *seen* a semi-useful decorator
> in code once (@contextlib.contextmanager) but still would prefer
> explicit dunder methods.

There are plenty of programs that don't need decorators, but in some
contexts, they are just beautiful. Building a web app in Flask or
Django involves functions that get decorated to say what endpoints
they handle, for instance. I've periodically used a simple decorator
plus some info in the function's docstring to do more magic. I'm not
sure where dunder methods come into this, though, as they're
completely unrelated.

ChrisA