Problems with copies (and references) to lists

[Michael Gilfix]

  I found this a little misleading. What's 's' have to do with
anything? Here's a couple of comments:

  * Check out 'import copy' and use that to copy lists.
  * Try using map to apply functions to various elements
    without any iteration. That might help some.

               -- Mike

On Wed, Apr 17 @ 17:12, bvdpoel at uniserve.com wrote:
> 
> Took awhile, but I do have the following bit of code working as it
> should. The doc string is misleading, but I'm not sure of how better to
> describe it out of context... The important thing is, it is giving the
> right result, and it is NOT changing the original list.
> 
> -------
> def doubleUp(a, fact):
>         """ Makes fact/2 copies of list [ [s, l, v,...] ].
>                 New copy has all values of l divided by fact/2 and
>                 copies of s set to s/2 and 50+(s/2).
> 		fact will always be a power of 2.
>         """
> 
>         new = a
>         while fact >1:
>                 b1 = []
>                 b2 = []
>                 for t in new[:]:
>                         n=t[:]          # this prevents munging our
> original
>                         n[0] /= 2
>                         n[1] /= 2
>                         b1+=[n[:]]      # [:] forces new copy of n!
>                         n[0] += 50
>                         b2+=[n]
>                 fact /=2
>                 new = b1 + b2
>         return new
> 
> a = [[0.0, 20.0, 66, 44],[50.0, 20.0, 55, 33]]
> print doubleUp(a, 2)
> print doubleUp(a,4)
> print a
> 
> --------
> 
> But, I'm wondering if it is at all efficient. Or even good python. Seems
> that the number of [:] needed just makes for ugly code.
> 
> -- 
> Bob van der Poel ** Wynndel, British Columbia, CANADA **
> EMAIL: bvdpoel at uniserve.com
> WWW:   http://users.uniserve.com/~bvdpoel
> 
> -- 
> http://mail.python.org/mailman/listinfo/python-list
`-> (bvdpoel)

-- 
Michael Gilfix
mgilfix at eecs.tufts.edu

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