rewrite for achieving speedup

[Jun.Jin.act+group.python@gmail.com]

On Apr 17, 11:25 pm, Steven Bethard <steven.beth... at gmail.com> wrote:
> Steve Holden wrote:
> > Johnny Blonde wrote:
> >> Hello Group!
>
> >> I really tried hard for two hours to rewrite the following expression
> >> (python 2.4):
> >> --------------------------
> >> teilnehmer = []
> >> for r in Reisen.select(AND(Reisen.q.RESVON <= datum, Reisen.q.RESBIS
> >>> = datum)):
> >>     for g in r.BUCHUNGEN:
> >>         for t in g.aktiveTeilnehmer:
> >>             teilnehmer.append(t)
> >> --------------------------
>
> >> to something like
> >> --------------------------
> >> teilnehmer = [x for x in ........]
> >> --------------------------
>
> >> Reisen is a SQLObject class, Reisen.select(...), aktiveTeilnehmer and
> >> BUCHUNGEN all are of the type SelectResults.
>
> >> unfortunately i just can´t figure it out to make it work.
> >> i hope someone maybe can help me?
>
> >> I hope to gain performance by rewriting it...
>
> >> Thanks a lot for your help!
>
> >  >>> lt = [[[1,2,3], [2,3,4]], [[3,4,5], [4,5,6]]]
> >  >>> lf = [c for a in lt for b in a for c in b]
> >  >>> lf
> > [1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 6]
>
> > Untested:
>
> > teilnehmer = [t for r in Reisen.select(AND(Reisen.q.RESVON <= datum,
> > reisen.q.RESBIS >= datum)) for g in r.BUCHUNGEN for t in
> > g.aktiveTeilnehmer]
>
> Note also that you can probably get most of the speedup above by binding
> the append method to a function-local name::
>
>      teilnehmer = []
>      append = teilnehmer.append
>      for r in Reisen.select(...):
>          for g in r.BUCHUNGEN:
>              for t in g.aktiveTeilnehmer:
>                  append(t)
>
> That's pretty much all a list comprehension is doing anyway.
>
> STeVe

hi steve,
why would binding to a function-local name speeds up performance?
sorry for asking such a simple question. many thanks.