generating points on a grid - efficiently

[simon place]

Rajarshi Guha wrote:
> Hi, 
>  I've written some code that takes a N lists of numbers (corresponding to
> axes) and generates a list of grid points (N dimensional grid) for the
> supplied axes. So as an example say my two axes are defined as
> 
> v1 = [1,2,3]
> v2 = [1,2,3]
> 
> My code will return to me a list of points: 
> 
> (1,1), (1,2), (1,3) ....(3,1), (3,2), (3,3)
> 

[[a,b] for a in v1 for b in v2]


> and so on. For 3 axes, I would obtain 27 points and so on.
> I've included the code below.


[[a,b,c] for a in v1 for b in v2 for c in v3]

etc.

then just pick the list comprehension from the count of axes.

or even build the list comp. required in a string and use exec()

> 
> My questions:
> 
> Firstly,  the code runs in exponential time. Is there any way to
> rewrite it to make it more efficient? It seems that this could be
> formulated as a recursive problem but I can't seem to get at it.
> 
> Secondly, it seems that the repeated use of copy.deepcopy() is very
> wasteful? Is there a way I can get around it?
> 
> Thanks,

alwys be exponential, but list comp. should be fast without much work.