RFC: Proposal: Deterministic Object Destruction

[Steven D'Aprano]

On Sat, 03 Mar 2018 12:37:08 -0500, Richard Damon wrote:

> With RAII and immediate destruction on end of scope, we can automate the
> release, without it and you need a lot of explicit code to manage these
> resources.

Not so much.

with resource_i_care_about() as rsrc:
    process(rsrc)


is hardly what I call "a lot of explicit code". Yes, there's some code in 
the context manager, but you write that *once* (if it isn't already 
written for you!) and you're done.

I know that laziness and hubris are programmer virtues, but there is 
still such a thing as *too much laziness*. RAII works in C++ where 
instances are allocated in the stack, but even there, if you have an 
especially long-lived function, your resources won't be closed promptly. 
In Python terms:

def function():
    x = open_resource()
    process(x)
    # and we're done with x now, but too lazy to explicitly close it
    sleep(10000) # Simulate some more work. Lots of work.
    return
    # and finally x is closed (2.8 hours after you finished using it)


The answer in C++ is "well don't do that then". The answer is Python is, 
"don't be so lazy, just use a with statement".

If you want deterministic closing of resources, with statements are the 
way to do it.


def function():
    with open_resource() as x:
        process(x)
    # and x is guaranteed to be closed
    sleep(10000) # Simulate some more work. Lots of work.
    return


-- 
Steve