[Numpy-discussion] List of Lists in C

Hanni Ali hanni.ali@gmail....
Mon Jan 26 02:47:25 CST 2009


Yes fair point, but when it's a empty list and new elements are replaced
with a new list instance it's fine, especially as [[]]*100000 is
significantly faster than [[] for i in xrange(100000)] as I was previously
doing.

In fact I think that's partly answered my question [[]]*x must create a list
of pointers pointing at the same list. Rather than [[] for i in
xrange(100000)] which must create a list of new separate lists instances.
Hence the significant difference in speed.

Hanni


2009/1/26 Matthieu Brucher <matthieu.brucher@gmail.com>

> Hi,
>
> Don't remember that you are using the same list in each element of the
> outer list. If you don't want this, use [[] for i in range(5)]. I
> don't think there is another way in C either (or too complicated).
>
> Matthieu
>
> 2009/1/26 Hanni Ali <hanni.ali@gmail.com>:
> > Hi,
> >
> > Quick question, I've been doing a fair bit of extension writing in C
> > recently, but wondered how best to implement:
> >
> >>>> l = [[]] * 5
> >
> > to create a list of a given length containing the initialization variable
> > desired.
> >
> > A loop seems the straight forward manner, but I would have thought there
> was
> > a more efficient way...
> >
> >
> > Currently I just do it in Python and pass through the already initialized
> > list as it seems perfectly efficient.
> >
> > Cheers,
> >
> > Hanni
> >
> >
> >
> > _______________________________________________
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> >
> >
>
>
>
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