preferring [] or () in list of error codes?

[samwyse]

On Jun 8, 10:06 pm, Chris Rebert <c... at rebertia.com> wrote:
> On Mon, Jun 8, 2009 at 6:57 PM, samwyse<samw... at gmail.com> wrote:
> > On Jun 8, 7:37 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
> >> On Jun 8, 4:43 pm, Ben Finney <ben+pyt... at benfinney.id.au> wrote:
> >> > m... at pixar.com writes:
> >> > > Is there any reason to prefer one or the other of these statements?
>
> >> > >         if e.message.code in [25401,25402,25408]:
> >> > >         if e.message.code in (25401,25402,25408):
>
> >> If you want to go strictly by the book, I would say he ought to be
> >> using a set since his collection of numbers has no meaningful order
> >> nor does it make sense to list any item twice.
>
> > As the length of the list increases, the increased speeds of looking
> > something up makes using a set makes more sense.  But what's the best
> > way to express this?  Here are a few more comparisons (using Python
> > 3.0)...
>
> >>>> S=lambda x:x in set((25401,25402,25408))
> >>>> dis(S)
> >  1           0 LOAD_FAST                0 (x)
> >              3 LOAD_GLOBAL              0 (set)
> >              6 LOAD_CONST               3 ((25401, 25402, 25408))
> >              9 CALL_FUNCTION            1
> >             12 COMPARE_OP               6 (in)
> >             15 RETURN_VALUE
> >>>> S=lambda x:x in{25401,25402,25408}
> >>>> dis(S)
> >  1           0 LOAD_FAST                0 (x)
> >              3 LOAD_CONST               0 (25401)
> >              6 LOAD_CONST               1 (25402)
> >              9 LOAD_CONST               2 (25408)
> >             12 BUILD_SET                3
> >             15 COMPARE_OP               6 (in)
> >             18 RETURN_VALUE
> >>>> S=lambda x:x in{(25401,25402,25408)}
> >>>> dis(S)
> >  1           0 LOAD_FAST                0 (x)
> >              3 LOAD_CONST               3 ((25401, 25402, 25408))
> >              6 BUILD_SET                1
> >              9 COMPARE_OP               6 (in)
> >             12 RETURN_VALUE
>
> > I conclude that using constructors is generally a bad idea, since the
> > compiler doesn't know if you're calling the builtin or something with
> > an overloaded name.  I presume that the compiler will eventually
> > optimize the second example to match the last, but both of them use
> > the BUILD_SET opcode.  I expect that this can be expensive for long
>
> Erm, unless I misunderstand you somehow, the second example will and
> should *never* match the last.
> The set {25401,25402,25408}, containing 3 integer elements, is quite
> distinct from the set {(25401,25402,25408)}, containing one element
> and that element is a tuple.
> set(X) != {X}; set([X]) = {X}

D'oh!  I was thinking about how you can initialize a set from an
iterator and for some reason thought that you could do the same with a
set constant.