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
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