zip as iterator and bad/good practices

From	Fabien <fabien.maussion@gmail.com>
Newsgroups	comp.lang.python
Subject	zip as iterator and bad/good practices
Date	2015-06-12 17:00 +0200
Organization	Aioe.org NNTP Server
Message-ID	<mles66$sk2$1@speranza.aioe.org> (permalink)

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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

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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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