[Python-ideas] Problems (and solutions?) in writing decorators

Sylvain MARIE sylvain.marie at se.com
Wed Mar 20 12:30:39 EDT 2019

All of your answers are true,

> (Chris)
> "my_decorator(x=foo)" is not going to look like "@my_decorator \n def foo".

That’s one of the many ways that `decopatch` uses to perform the disambiguation, indeed. But that’s already the user helping the lib, not the other way round

> (Christopher)
> @something applied on def fun is exactly the same as something(fun)

True. However applying decorator manually is already for advanced users, so users of a decopatche-d decorator will not mind calling something()(fun). In fact it is consistent with when they use it with arguments : something(arg)(fun).

Another criterion is : how easy would it be to implement an inspect.is_decorator_call(frame) method returning True if and only if frame is the @ statement ? If that’s fairly easy, well, I’m pretty sure that this is good stuff. From a naïve user, not accustomed with the long history of this language, is very strange that an operator such as @ (the decorator one, not the other one) is completely not detectable by code, while there are so many hooks available in python for all other operators (+, -, etc.).

Eventually that’s obviously your call, I’m just there to give feedback from what I see of the python libs development community.


De : Python-ideas <python-ideas-bounces+sylvain.marie=se.com at python.org> De la part de Christopher Barker
Envoyé : mercredi 20 mars 2019 06:50
À : Greg Ewing <greg.ewing at canterbury.ac.nz>
Cc : python-ideas <python-ideas at python.org>
Objet : Re: [Python-ideas] Problems (and solutions?) in writing decorators

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def fun():

Is exactly the same as:

def fun()

fun = something(fun)

So you can’t make a distinction based whether a given usage  is as a decoration.


On Tue, Mar 19, 2019 at 12:26 PM Greg Ewing <greg.ewing at canterbury.ac.nz<mailto:greg.ewing at canterbury.ac.nz>> wrote:
Sylvain MARIE via Python-ideas wrote:
> `my_decorator(foo)` when foo is a callable will always look like
> `@my_decorator` applied to function foo, because that's how the language is
> designed.

I don't think it's worth doing anything to change that. Everywhere
else in the language, there's a very clear distinction between
'foo' and 'foo()', and you confuse them at your peril. I don't see
why decorators should be any different.

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