[Python-ideas] "atexit" equivalent for functions in contextlib

[Nick Coghlan]

On 30 Jan 2015 12:29, "Nikolaus Rath" <Nikolaus at rath.org> wrote:
>
> Nick Coghlan <ncoghlan-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org> writes:
> > On 29 January 2015 at 15:49, Nikolaus Rath <
Nikolaus-BTH8mxji4b0 at public.gmane.org> wrote:
> >> It's not a lot of code, but my feeling is that not anyone who might be
> >> interested in an "on_return" functionality would be able to come up
with
> >> this right away.
> >
> > What does it gain you other than saving a level of indentation over
> > the form with an explicit context manager?
>
> Nothing. But if that's not a good enough reason, why do we have
> contextlib.ContextDecorator?

I'm occasionally inclined to consider accepting that proposal a mistake on
my part. It's certainly borderline.

That said, the main advantage that applies to ContextDecorator but not to
this proposal is lightweight addition of "before & after" behaviour like
serialisation, tracing or logging to a function - you just decorate it
appropriately without touching any other part of the function. That's a
useful thing to encourage, and it's handy that generator based context
managers can be used that way by default.

This proposal is different:

* it's inherently coupled to the function body (you need to change the
function signature, and allocate resources inside the function for later
cleanup)
* it's adding information about an implementation detail (how the function
manages resource deallocation) to a header that's ideally focused on
declaring the function's interface and externally visible behaviour

Cheers,
Nick.

>
> Best,
> -Nikolaus
>
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