Re: Importing variables non-deterministic?

From	Dave Angel <davea@davea.name>
Subject	Re: Importing variables non-deterministic?
Date	2013-08-19 12:33 +0000
References	(4 earlier) <5211D464.5090303@rece.vub.ac.be> <CAPTjJmqvzkuZ8Pmux=K6SSPBeLuDQiD99t7g_pAwujCfb2ON4g@mail.gmail.com> <5211DF6C.6030603@rece.vub.ac.be> <CAPTjJmoATrm+Ke5LNu3zJ-2YppBDqOSTXRP+USwNWrpH64r0sQ@mail.gmail.com> <52120783.8040008@rece.vub.ac.be>
Newsgroups	comp.lang.python
Message-ID	<mailman.28.1376915632.19984.python-list@python.org> (permalink)

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Antoon Pardon wrote:

> Op 19-08-13 11:18, Chris Angelico schreef:
    <snip>
>> The issue
>> was regarding imports, and it's perfectly safe to import a constant,
>> even if the interpreter doesn't protect you from then being a total
>> idiot and changing it.
>
> Python doesn't have constants, so you statement about importing a
> constant doesn't make sense. The point is that python doesn't provide
> the mechanism for protecting names against reassignments. So you
> don't know whether the variable you think of as a constant is so
> in reality. And this from a pure language definition point of view.
> That you can use tools that make the interpreter no longer behave
> as the language should, doesn't negate that.
>

Who cares what the language "protects?"  I don't know any language
whose protections can't be at least partially bypassed by clever
foot-shooters.  In any case, we all know that Python doesn't protect
constants, so we're free to use the word in a friendlier way.

A Python constant is what I use as a constant.  I follow Pep-8 and make
it all caps.  So in any library I write struct_global.y  would be a bug
or a design flaw.  (And with a single character name like that, it
wouldn't be global in any case.  Single character names are reserved
for play code and for short loops)

And if I subsequently change it in my calling code, it isn't a
constant any more.  If I rebind the name, it's not even the same
variable any more.

That's a bug, not an exception to the rule "don't use global variables."

I also accept as a constant those values which are initialized
sufficiently early in the code that most places will only ever see the
final value.  Those may be global without worry.

-- 
DaveA

Thread

Importing variables non-deterministic? tmellman@googlemail.com - 2013-08-17 07:25 -0700
  Re: Importing variables non-deterministic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-17 15:01 +0000
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 09:14 +0200
    Re: Importing variables non-deterministic? Dave Angel <davea@davea.name> - 2013-08-19 07:45 +0000
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 10:16 +0200
      Re: Importing variables non-deterministic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-19 16:57 +0000
        Re: Importing variables non-deterministic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-19 17:16 +0000
          Re: Importing variables non-deterministic? Chris Angelico <rosuav@gmail.com> - 2013-08-19 18:25 +0100
        Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 19:40 +0200
    Re: Importing variables non-deterministic? Chris Angelico <rosuav@gmail.com> - 2013-08-19 09:32 +0100
      Re: Importing variables non-deterministic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-19 17:05 +0000
        Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 22:34 +0200
          Re: Importing variables non-deterministic? Steven D'Aprano <steve@pearwood.info> - 2013-08-20 05:48 +0000
            Re: Importing variables non-deterministic? wxjmfauth@gmail.com - 2013-08-19 23:40 -0700
            Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-20 08:55 +0200
              Re: Importing variables non-deterministic? wxjmfauth@gmail.com - 2013-08-20 00:31 -0700
                Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-20 09:55 +0200
                Re: Importing variables non-deterministic? wxjmfauth@gmail.com - 2013-08-20 02:15 -0700
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 11:03 +0200
    Re: Importing variables non-deterministic? Chris Angelico <rosuav@gmail.com> - 2013-08-19 10:18 +0100
    Re: Importing variables non-deterministic? Peter Otten <__peter__@web.de> - 2013-08-19 11:49 +0200
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 13:54 +0200
    Re: Importing variables non-deterministic? Dave Angel <davea@davea.name> - 2013-08-19 12:33 +0000
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 16:55 +0200
    Re: Importing variables non-deterministic? Chris Angelico <rosuav@gmail.com> - 2013-08-19 16:04 +0100
    Re: Importing variables non-deterministic? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-19 19:25 +0200
    Re: Importing variables non-deterministic? Ben Finney <ben+python@benfinney.id.au> - 2013-08-20 11:14 +1000

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