[Python-ideas] set.add could return True or False

[Matt Joiner]

This is an example only.
On Mar 15, 2012 1:46 AM, "Andrew Svetlov" <andrew.svetlov at gmail.com> wrote:

> You still can get race condition:
>
> if b.add(a):
>   # some thread removes a from b before do_c call...
>   do_c()
>
> Explicit lock is still required for your case.
>
> On Wed, Mar 14, 2012 at 10:36 AM, Matt Joiner <anacrolix at gmail.com> wrote:
> > set.add(x) could return True if x was added to the set, and False if x
> > was already in the set.
> >
> > Adding an element that is already present often constitutes an error in
> my code.
> >
> > As I understand, set.add is an atomic operation. Having set.add return
> > a boolean will also allow EAFP-style code with regard to handling
> > duplicates, the long winded form of which is currently:
> >
> > if a not in b:
> >    b.add(a) <-- race condition
> >    do_c()
> >
> > Which can be improved to:
> >
> > if b.add(a):
> >    do_c()
> >
> > Advantages:
> >  * Very common code pattern.
> >  * More concise.
> >  * Allows interpreter atomicity to be exploited, often removing the
> > need for additional locking.
> >  * Faster because it avoids double contain check, and can avoid locking.
> > _______________________________________________
> > Python-ideas mailing list
> > Python-ideas at python.org
> > http://mail.python.org/mailman/listinfo/python-ideas
>
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