On 10/12/2019 17:18, R.Wieser wrote:
Chris,
Okay. What should happen when you do this?
x = 5
del x
Should the integer 5 be deleted?
Yep.
What do you think happens instead ? I've not seen you explain or support
anything in that regard, not even now.
As it happens, the object that is the integer 5 *isn't* deleted. Once
again, you are making assertions based on what you believe to be true,
despite having been told otherwise. That's fair enough, but you then
give those assertions the weighting of fact.
There is a bit of a problem with the above though: It has got zero to do
with the __del__ I was talking about.
On the contrary, it's exactly the point. You are asserting behaviour
that you are not guaranteed. It happens that current versions of
CPython conform to your expectations. I have a vague and unreliable
recollection that earlier versions didn't. Other Python interpreters
may or may not. The language description does not give you that
guarantee, so relying on it is at best foolish.
I've not seen you point out any
mistake with my example (pointing out race contition problems) either.
Greg Ewing did:
"In that case, it was only working by accident. You were unwittingly
relying on the garbage collector to immediately clean up the object
as soon as the last reference to it disappeared. That happens to be
true currently in CPython (which uses reference counting), but it's
not guaranteed by the language."
Unless you're referring to some other example. It's a bit hard to tell
without the context.
Not a smooth move bro. Not a smooth move /at all/ :-(
Words fail me.
So the language designers couldn't possibly have been so stupid
as to do things this way, but you're going to ignore what they did?
Actually, they didn't.
Did you know you can disable the garbage collector ? Well, you can. Guess
what I saw when I disabled it, created a class instance and than deleted it
again. Yup, the "print" command I placed in the "__del__" method did
actually show output - something that, according to you, could/should never
happen ...
What you disabled wasn't the garbage collector, it was the garbage
collector's periodic background run to detect reference cycles and
delete them when they have no external references. The garbage
collector itself ran just fine when your instance's reference count
reached zero, exactly as everyone has been saying to you.
And to repeat, you have *no* guarantee *at all* in the language spec
that this will happen. The garbage collector could have waited until it
was short of space before deleting the object, for example, which might
not happen until your script terminates.
--
Rhodri James *-* Kynesim Ltd
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