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Re: zip as iterator and bad/good practices

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On 12/06/2015 16:00, Fabien wrote:
> Folks,
>
> I am developing a program which I'd like to be python 2 and 3
> compatible. I am still relatively new to python and I use primarily py3
> for development. Every once in a while I use a py2 interpreter to see if
> my tests pass through.
>
> I just spent several hours tracking down a bug which was related to the
> fact that zip is an iterator in py3 but not in py2. Of course I did not
> know about that difference. I've found the izip() function which should
> do what I want, but that awful bug made me wonder: is it a bad practice
> to interactively modify the list you are iterating over?
>
> I am computing mass fluxes along glacier branches ordered by
> hydrological order, i.e. branch i is guaranteed to flow in a branch
> later in that list. Branches are objects which have a pointer to the
> object they are flowing into.
>
> In pseudo code:
>
> for stuff, branch in zip(stuffs, branches):
>      # compute flux
>      ...
>      # add to the downstream branch
>      id_branch = branches.index(branch.flows_to)
>      branches[id_branch].property.append(stuff_i_computed)
>
> So, all downstream branches in python2 where missing information from
> their tributaries. It is quite a dangerous code but I can't find a more
> elegant solution.
>
> Thanks!
>
> Fabien
>

Start here https://docs.python.org/3/howto/pyporting.html

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:00 +0200
  Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:05 +0200
  Re: zip as iterator and bad/good practices Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-12 09:26 -0600
    Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:34 +0200
    Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:59 +0200
  Re: zip as iterator and bad/good practices Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-12 17:22 +0100
  Re: zip as iterator and bad/good practices Laura Creighton <lac@openend.se> - 2015-06-12 22:34 +0200
  Re: zip as iterator and bad/good practices Terry Reedy <tjreedy@udel.edu> - 2015-06-12 19:27 -0400
  Re: zip as iterator and bad/good practices Terry Reedy <tjreedy@udel.edu> - 2015-06-12 19:43 -0400
    Re: zip as iterator and bad/good practices sohcahtoa82@gmail.com - 2015-06-12 17:02 -0700
      Re: zip as iterator and bad/good practices Chris Angelico <rosuav@gmail.com> - 2015-06-13 10:26 +1000
        Re: zip as iterator and bad/good practices sohcahtoa82@gmail.com - 2015-06-12 17:39 -0700
  Re: zip as iterator and bad/good practices jimages <jimages123@gmail.com> - 2015-06-13 13:32 +0800
    Re: zip as iterator and bad/good practices Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-13 07:17 +0000
      Re: zip as iterator and bad/good practices Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-06-13 13:48 +0100
        Re: zip as iterator and bad/good practices Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-13 16:16 +0000

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