[Python-ideas] Re: Have del return a value

[Dom Grigonis]

Also, check out https://docs.python.org/3/library/weakref.html 


Maybe it will not provide exactly what you indicated, but might get some ideas 
how to do things differently.

—
Now is better than never. Although never is often better than *right* now. == 
Deferred Evaluation
—
Dg


> On 9 Sep 2023, at 09:02, Jeff Allen  wrote:
> 
> On 06/09/2023 03:47, Daniel Walker wrote:
>> Perhaps this is a solution in search of a problem but I recently encountered 
>> this situation in one of my projects.
>> 
>> I have an object, foo, which, due to the references it contains, I'd rather 
>> not keep around longer than necessary.
>> 
>> I use foo to instantiate another object:
>> 
>> bar = Bar(foo)
>> 
>> bar is free to manipulate foo however it wants and even del it if necessary. 
>>  However, since the foo name is still around, those resources won't get 
>> cleaned up even if bar is done with them.  The simple solution is
>> 
> It's a neat idea but there are other ways that may be better.
> 
> I assume foo is a "specification", that is, an object you configure through a 
> number of optional calls or attribute assignments, then pass to Bar() as a 
> design alternative to Bar() having a complicated set of arguments. A pattern 
> often used is the fluent API:
> 
> bar = Bar(Foo().a().b(42).c('penguin'))
> 
> Now only Bar has a reference to the Foo you made.
> 
> But foo is not necessarily destroyed immediately the last reference to it is 
> dropped, even with del or when nameless in the fluent API. If you wanted to 
> be certain, you could make Foo a context manager to use like this:
> 
> with Foo() as foo:
> foo.a()
> foo.b(42)
> foo.c('penguin')
> bar = Bar(foo)
> bar.do_stuff()
> (Think I got that right. Not tried it.) Now Foo.__exit__ can be made to 
> properly tear down the resources in a foo.
> 
> -- 
> 
> Jeff Allen
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[Python-ideas] Re: Have del return a value

[Jeff Allen]

On 06/09/2023 03:47, Daniel Walker wrote:
Perhaps this is a solution in search of a problem but I recently 
encountered this situation in one of my projects.


I have an object, foo, which, due to the references it contains, I'd 
rather not keep around longer than necessary.


I use foo to instantiate another object:

    bar = Bar(foo)

bar is free to manipulate foo however it wants and even del it if 
necessary.  However, since the foo name is still around, those 
resources won't get cleaned up even if bar is done with them.  The 
simple solution is



It's a neat idea but there are other ways that may be better.

I assume foo is a "specification", that is, an object you configure 
through a number of optional calls or attribute assignments, then pass 
to Bar() as a design alternative to Bar() having a complicated set of 
arguments. A pattern often used is the fluent API:


bar = Bar(Foo().a().b(42).c('penguin'))

Now only Bar has a reference to the Foo you made.

But foo is not necessarily destroyed immediately the last reference to 
it is dropped, even with del or when nameless in the fluent API. If you 
wanted to be certain, you could make Foo a context manager to use like this:


with Foo() as foo:
    foo.a()
    foo.b(42)
    foo.c('penguin')
    bar = Bar(foo)
bar.do_stuff()

(Think I got that right. Not tried it.) Now Foo.__exit__ can be made to 
properly tear down the resources in a foo.


--

Jeff Allen
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