A "scopeguard" for Python

[Alf P. Steinbach]

* Robert Kern:
> On 2010-03-04 09:48 AM, Alf P. Steinbach wrote:
>> * Jean-Michel Pichavant:
>>> Alf P. Steinbach wrote:
>>>>> From your post, the scope guard technique is used "to ensure some
>>>>> desired cleanup at the end of a scope, even when the scope is exited
>>>>> via an exception." This is precisely what the try: finally: syntax
>>>>> is for.
>>>>
>>>> You'd have to nest it. That's ugly. And more importantly, now two
>>>> people in this thread (namely you and Mike) have demonstrated that
>>>> they do not grok the try functionality and manage to write incorrect
>>>> code, even arguing that it's correct when informed that it's not, so
>>>> it's a pretty fragile construct, like goto.
>>>
>>> You want to execute some cleanup when things go wrong, use try except.
>>> You want to do it when things go right, use try else. You want to
>>> cleanup no matter what happen, use try finally.
>>>
>>> There is no need of any Cleanup class, except for some technical
>>> alternative concern.
>>
>> Have you considered that your argument applies to the "with" construct?
>>
>> You have probably not realized that.
>>
>> But let me force it on you: when would you use "with"?
> 
> When there is a specific context manager that removes the need for 
> boilerplate.

That's "cleanup no matter what happen".


>> Check if that case is covered by your argument above.
>>
>> Now that you've been told about the "with" angle, don't you think it's a
>> kind of weakness in your argument that it calls for removing "with" from
>> the language?
> 
> No, it only argues that "with Cleanup():" is supernumerary.

I don't know what "supernumerary" means, but to the degree that the argument 
says anything about a construct that is not 'finally', it says the same about 
general "with".

So whatever you mean by supernumerary, you're saying that the argument implies 
that "with" is supernumerary.

This is starting to look like some earlier discussions in this group, where even 
basic logic is denied.


Cheers,

- Alf