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Date: Tue, 16 Apr 2013 17:37:01 +0200
From: aaB <mecagonoisician@gmail.com>
To: py-list <python-list@python.org>
Subject: a couple of things I don't understand wrt lists
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Xref: csiph.com comp.lang.python:43675

hello,

I am a beginner programmer. I started learning programming about a year and a
half ago, using C. I picked up python a few months ago, but only wrote very few
scripts.

I am currently trying to learn more about the python way of doing things by
writing a script that generates png images using a 1D cellular automaton.

While writing preliminary code for that project, I ran into a behaviour that I
don't understand.
I am using python 2.7 on a linux system.

I represent the CA's rule with a list of integers, of value 1 or 0.
Here is the function I use to generate the list:

def get_rule(rulenum):
  rule = []
  while rulenum > 0:
    rule.append(rulenume % 2)
    rulenum /= 2
  while len(rule) < 8:
    rule.append(0)
  rule.reverse()
  return rule

if i call it by writing:

rule = getrule(int(8))

and then call:

print rule

the output is good:

[0, 0, 0, 0, 1, 0, 0, 0]


I then tried to print each item of the list using a for loop:

for i in range(rule):
  print rule[i]

the output is, as expected:
0
0
0
0
1
0
0
0

but when I do:

for i in rule:
  print rule[i]

I get the "complement":
1
1
1
1
0
1
1
1

There must be something I didn't understand correctly in the for statement, but
I really can't think of a reason why the output is what it is.
I tried this using the interactive console, and the results are the same,
whatever the length of the list, i always get the complement of my bit pattern.

Any pointers to help me understand this would be appreciated.
I am also running into an other issue with this script, but I'd rather
understand this before asking further questions.

Thanks, and sorry for the rather long post.