expression in an if statement

[ernest]

On 19 Ago, 08:40, Frederic Rentsch <anthra.nor... at bluewin.ch> wrote:
> On Thu, 2010-08-19 at 00:12 +0200, Thomas Jollans wrote:
> > On Wednesday 18 August 2010, it occurred to John Nagle to exclaim:
> > > On 8/18/2010 11:24 AM, ernest wrote:
> > > > Hi,
>
> > > > In this code:
>
> > > > if set(a).union(b) == set(a): pass
>
> > > > Does Python compute set(a) twice?
>
> > >     CPython does.  Shed Skin might optimize.  Don't know
> > > about Iron Python.
>
> > I doubt any actual Python implementation optimizes this -- how could it?
>
> And why should it if a programmer uses its facilities inefficiently. I
> would write
>
> >>> if set(a).issuperset (b): pass
>
> Frederic

Yes, maybe the example is silly, but situations like this arise
frequently and it's good to know.

Thanks for the answers.

Ernest